Methods and apparatus for guiding medical care based on sensor data from the gastrointestinal tract

ABSTRACT

Methods and apparatus for guiding medical care based on sensor data from the gastrointestinal tract are described utilizing an apparatus which can be used with enteral feeding. Generally, the apparatus includes an elongated body having a length configured for insertion into a stomach and at least one pair of electrodes located along the length of the elongated body and positionable for placement within the stomach. A controller in electrical communication with the at least one pair of electrodes is included and the control may also be configured to measure a conductivity or impedance between the pair of electrodes and to determine a gastric residual volume of the stomach based on the measured conductivity or impedance.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.17/810,439 filed Jul. 1, 2022, which is a continuation of Ser. No.15/811,433 filed Nov. 13, 2017, which is a continuation of InternationalPatent Application No. PCT/US2016/033335 filed May 19, 2016, whichclaims the benefit of priority to U.S. Provisional Application No.62/164,488 filed May 20, 2015, U.S. Provisional Application No.62/258,329 filed Nov. 20, 2015, U.S. Provisional Application No.62/185,697 filed Jun. 28, 2015, U.S. Provisional Application No.62/312,257 filed Mar. 23, 2016, each of which is incorporated herein byreference in its entirety.

FIELD OF THE INVENTION

The present invention relates to the measuring of gastric volume,gastric emptying, reflux, and feeding tube placement/monitoring.

INCORPORATION BY REFERENCE

All publications and patent applications mentioned in this specificationare herein incorporated by reference to the same extent as if each suchindividual publication or patent application were specifically andindividually indicated to be so incorporated by reference.

BACKGROUND OF THE INVENTION

The provision of adequate nutrition is widely recognized as importantfor recovery from acute illnesses. Nutritional support is often requiredfor intensive care unit (ICU) patients, hospital ward patients, andnursing home patients. Results from 14 randomized trials demonstrated41% lower mortality and 27% fewer infectious complications in ICUpatients randomized to early (vs. delayed) enteral nutrition accordingto Heyland et al, “Review of ICU Early vs. Delayed Feeding RandomizedTrials.” JPEN, 2003; 27:355-73, hereafter “Heyland” which is herebyincorporated in its entirety herein by reference. Patients receivingearly enteral nutrition had a shorter ICU length of stay (4.7 vs 8.5days), shorter time on the ventilator (3.0 vs 6.0 days), and reducedmortality (5.5% vs 38.9%) according to Woo et al., “Early vs delayedenteral nutrition in critically ill medical patients.” Nutr Clin Pract.2010 April; 25(2):205-11, hereafter “Woo” which is hereby incorporatedin its entirety herein by reference. Early nutrition was associated witha 20% decrease in ICU mortality and 25% decrease in hospital mortality,but had an attendant 18% increase in the incidence of pneumoniaaccording to Artinian et al, “Effects of early enteral feeding on theoutcome of critically ill mechanically ventilated medical patients.”Chest. 2006 April; 129(4):960-7, hereafter “Artinian” which is herebyincorporated in its entirety herein by reference. The Society ofCritical Care Medicine (SCCM) and the American Society of Parenteral andEnteral Nutrition (ASPEN) guidelines recommend early nutrition.

While guidelines recommend feeding patients early, many acute carepatients may not be ready for nutrition, as evidenced by a study whereup to 62.8% of ICU patients exhibited signs of feeding intolerance, andwhere feeding intolerance was subsequently associated with highermortality (31% vs 16%, p<0.001) according to J C Montejo, “Enteralnutrition-related gastrointestinal complications in critically illpatients: a multicenter study.” Crit Care Med. 1999 August;27(8):1447-53, hereafter “Montejo” which is hereby incorporated in itsentirety herein by reference.

Clinicians are fearful of feeding patients too early since they may beat risk for aspirating gastric contents into the lungs. Pulmonaryaspiration is very common in acute care patients. For example, 62% ofhospitalized elderly patients aspirate according to Murry et al., “Thesignificance of accumulated oropharyngeal secretions and swallowingfrequency in predicting aspiration.” Dysphagia. 1996 Spring;11(2):99-103, hereafter “Murry” which is hereby incorporated in itsentirety herein by reference. Similarly, it has been found that 38% ofstroke patients aspirate; in more than ⅔ of these patients, aspirationgoes unrecognized by the clinicians caring for them according to Danielset al, “Aspiration in patients with acute stroke.” Arch Phys MedRehabil. 1998 Jan; 79(1):14-9, hereafter “Daniels” which is herebyincorporated in its entirety herein by reference. Another study foundthat 50% of patients with stroke or brain injury aspirate, according toVeis et al, “Swallowing disorders in persons with cerebrovascularaccident.” Arch Phys Med Rehabil. 1985 June; 66(6):372-5, hereafter“Veis” which is hereby incorporated in its entirety herein by reference.

Aspirating these gastric contents into the lungs can result indevastating consequences, such as chemical pneumonitis or pneumonia, oreven death due to asphyxiation. For example, aspiration pneumoniaoccurred in 19% of elderly hospitalized patients and 44% of nursing homepatients according to Langmore et al, “Predictors of aspirationpneumonia in nursing home residents.” Dysphagia. 2002 Fall;17(4):298-307, hereafter “Langmore” which is hereby incorporated in itsentirety herein by reference. Stroke patients who aspirate had a 6.95times greater risk of developing pneumonia than patients who did notaspirate according to Holas et al, “Aspiration and relative risk ofmedical complications following stroke.” Arch Neurol. 1994 October;51(10):1051-3, hereafter “Holas” which is hereby incorporated in itsentirety herein by reference. Pneumonitis (i.e., sterile inflammation)is often misdiagnosed as pneumonia, since pneumonia and pneumonitis(triggered by the presence of gastric juice and particulate matter) canbe associated with similar clinical findings. Furthermore, sterilepneumonitis can lead to the development of pneumonia. Thus, 40% of casesof suspected pneumonia in nursing home residents were classified aspneumonitis based on definite or suspected aspiration event according toMylotte et al, “Pneumonia versus aspiration pneumonitis in nursing homeresidents: prospective application of a clinical algorithm.” J AmGeriatr Soc. 2005 May; 53(5):755-61, hereafter “Mylotte” which is herebyincorporated in its entirety herein by reference. Overall, highmortality rates (>50%) are associated with aspiration pneumonia andpneumonitis according to DeLegge et al, “Aspiration pneumonia:incidence, mortality, and at-risk populations.” JPEN J Parenter EnteralNutr. 2002 November-December; 26(6 Suppl):S19-24; discussion S24-5,hereafter “Delegge” which is hereby incorporated in its entirety hereinby reference.

Many acute care patients are at greater risk for developingcomplications from aspiration because of trouble swallowing, also calleddysphagia, impaired gag reflex and/or a compromised immune system. Theseinclude patient populations such as the elderly, patients who areheavily sedated, patients suffering from stroke, traumatic brain injury,brain tumor, or head and neck cancer. The following are risk factors foraspiration: gastroesophageal reflux, increased age with physiologicinsult, cerebral vascular accident, decreased consciousness,gastroparesis, tracheal intubation, naso/oral enteral intubation,enteral feeding, anesthesia, supine position, seizure according toDeLegge.

Among patients, who are receiving enteral nutrition via (continuous orintermittent) administration of a tube feeding formula into the stomachthrough an orogastric or (more commonly) a nasogastric feeding tube, therisk of aspiration of gastric contents is increased when gastricemptying into the small intestine is impaired. The most common cause ofimpaired or delayed gastric emptying is gastric ileus (i.e., gastricdysmotility). When patients are receiving enteral nutrition viacontinuous administration of a tube feeding formula through a feedingtube, clinicians (nurses and physicians) commonly seek to preventaspiration by periodic measurements of “gastric residual volume” or GRV.Typically, GRV is estimated by periodically connecting a large syringeto the orogastric or nasogastric feeding tube, and applying suction toremove the gastric contents and then measuring the volume of contentsthereby removed. Often, enteral feeding is temporarily discontinued ifthe measured GRV is greater than some (arbitrarily determined) thresholdvalue (e.g., 200 mL or 300 mL).

This fear of aspiration often results in clinicians underfeedingpatients. For example, up to 45% of ICU patients do not receivenutrition during the first 3-5 days after admission to the unit,according to Nguyen et al, “The impact of delaying enteral feeding ongastric emptying, plasma cholecystokinin, and peptide YY concentrationsin critically ill patients.” Crit Care Med. 2008 May; 36(5):1469-74,hereafter “Nguyen” which is hereby incorporated in its entirety hereinby reference. Surgical ICU patients on average started enteral nutritionafter 57.8 hours according to Drover et al, “Nutrition Therapy for theCritically Ill Surgical Patient: We Need To Do Better!” JPEN J ParenterEnteral Nutr 2010 34: 644, hereafter “Drover” which is herebyincorporated in its entirety herein by reference.

Gastric contents typically are acidic. If acidic gastric contents enterthe esophagus, the result can be the symptoms of acid reflex, such asheartburn, acid indigestion, and burning pain. If the acid refluxprogresses further up the esophagus, it can possibly enter the tracheaand lungs and result in pulmonary aspiration.

Thus, while clinicians want to feed patients early, they are concernedthat patients might be at risk for reflux. Unfortunately, there are noreliable signs to help clinicians determine whether patients areexperiencing reflux or may be at risk. The patient population appears tobe quite variable with respect to which patients are exhibiting refluxand how much reflux these patients are experiencing. In one study, 22 of24 (91%) of ventilated pediatric ICU patients exhibited reflux accordingto Abdel-Gawad et al, “Gastroesophageal reflux in mechanicallyventilated pediatric patients and its relation to ventilator-associatedpneumonia.” Crit Care. 2009; 13(5):R164, hereafter “Abdel-Gawad” whichis hereby incorporated in its entirety herein by reference. In this samestudy by Abdel-Gawad, pneumonia patients had more episodes (6.5) andlonger total reflux time (50 min) compared to non-pneumonia patients (1episode, 3 min). In another study, 6 of 11 (55%) of adult mechanicallyventilated ICU patients experienced 25 reflux events, as measured byimpedance monitoring according to Nind et al, “Mechanisms ofgastroesophageal reflux in critically ill mechanically ventilatedpatients.” Gastroenterology. 2005 March; 128(3):600-6, hereafter “Nind”which is hereby incorporated in its entirety herein by reference. Nindfurther described how there was significant inter-patient variabilitywith one patient having 13 reflux events and five patients having noreflux events. The incidence in the overall ICU population is likelyhigher since the Nind study consisted only of a “healthier” populationalready tolerating enteral nutrition, plus the data were only recordedfor one hour prior to feeding and five hours during NG feeding. Inanother study, 30 of 36 (83%) mechanically ventilated ICU patients aged1 month to 7 years of age experienced 338 episodes of reflux, with amean of 9.3 episodes per patient (SD 16, median 2, range 1-79) accordingto Solana et al, “Multichannel intraluminal impedance to studygastroesophageal reflux in mechanically ventilated children in the first48 h after PICU admission.” Nutrition. 2013 July-August; 29(7-8):972-6,hereafter “Solana” which is hereby incorporated in its entirety hereinby reference. Solana also describes how 16 of the 338 episodes werefound to reach the superior channels via impedance measurement. Theincidence is likely higher since no feeding was done during themeasurement timeframe.

Most commonly, feeding tubes are small bore (5 French to 12 Frenchoutside diameter) plastic tubes. Very small bore tubes are intrinsicallyvery flexible, and therefore are difficult to pass. Accordingly, verysmall tubes often are provided with a thin wire stiffener, or stylet,located in the lumen. The stiffening wire, which facilitates insertionof the tube, is removed after the tube has been correctly positioned inthe stomach. Most commonly, feeding tubes are inserted into one of thenares. The tube is advanced sequentially through the nasopharynx,oropharynx, hypopharynx, and esophagus, ultimately leading to placementof the distal tip of the tube in the lumen of the stomach. Occasionally,as the tube is being advanced through the hypopharynx, the tube goesthrough the larynx and enters the trachea, rather than passing into theesophagus. If the feeding tube has a wire stylet and is advanced all theway down the tracheobronchial tree into a distal subsegmentalbronchiole, then the lung parenchyma can be perforated, leading topneumothorax or even formation of a bronchopleural fistula. Even if thetube is not stiffened with a stylet or is not advanced into the distaltracheobronchial tree, the introduction of tube feeding formula into theairways (trachea, mainstem bronchi, or segmental bronchi), can havecatastrophic consequences, including pneumonitis, pneumonia or evendeath. Because clinicians are aware of the risk of inadvertentlyintroducing tube feeding formula into the airways, most institutionsmandate radiographic confirmation that the tip of the feeding tube isproperly located in the stomach (or the small intestine) prior toinitiating tube feeding.

Enteral feeding through a feeding tube allows patients to receivenutrition when he/she cannot receive nutrition through the mouth, cannotswallow safely or to provide supplemental nutrition. Current standard ofcare requires periodic monitoring of the gastric residual volume (GRV)after feeding. GRV is the volume of residual gastric contents thatremain in the stomach after a certain period of time has elapsed afterfeeding via a feeding tube. The concern is that high GRV values mayindicate pulmonary aspiration, a critical issue that could lead topneumonia with serious consequences. Usually these GRV measurementsoccur every 4-6 hours, and particularly during the first few days ofenteral feeding to allow acceptance of the feeding tube.

The current standard method of determining GRV is via aspiration from anasogastric tube. There are several issues with the current methods ofdetermining GRV including:

1) Aspiration of contents to measure GRV is a burden on nursing staff.Even with expertise in the procedure, the process takes 5 minutes. Withthis repeated every 4-6 hours for every patient requiring GRVmonitoring.

2) The process of aspirating gastric contents through manual mechanicalmeans may increase the incidence of pulmonary aspiration.

3) Lack of standardization of means to manually measure GRV, whetherthrough aspiration by syringe, low-wall suction, gravity drainage orother method, introduce errors in measurement.

A solution is needed which addresses these and other issues withmeasuring GRV in patients.

SUMMARY OF THE INVENTION

The present invention is a GRV measuring device and methods whichdetermine the volume of gastric content by introduction of at least oneadditive component (a GRV indicator) that is dispersed and then changesa physical (chemical, electrical, thermal, mechanical, optical, etc.)characteristic within the stomach contents by a measureable degree. Thedegree of change of this physical characteristic, and/or the rate ofreturn to the previous state, may be used to determine the GRV of apatient. If the GRV is small, the magnitude of change will likely begreater, and the rate of change of this physical characteristic back tobaseline will be slower. If the GRV is large, the magnitude of changewill likely be smaller, and the rate of return to baseline will befaster. The determined GRV can also be used to automatically orsemi-automatically control the patient's feeding rate and/or volumeand/or frequency to adequately nourish the patient but avoidcomplications. The physical characteristic(s) may also be used to detectthat the feeding catheter or tube is in the correct location (i.e.stomach vs lung or esophagus). Note that the term “GRV” may refer toGastric Residual Volume or Gastric Emptying or Gastric residual feed.Gastric emptying in an indicator of gastric volume, or rate of gastricemptying, either of which can indicate when a patient needs to be fed.The GRV measuring device embodiments disclosed here may measure gastricresidual volume, or gastric emptying or gastric residual feed.Specifically, the GRV measuring device embodiments disclosed her maymeasure gastric food percentage (food vs gastric fluids), gastricresidual volume, and/or gastric residual food.

One variation of an apparatus for determining a gastric residual volumemay generally comprise an elongate tube defining at least one lumentherethrough, a medium having one or more GRV indicators in fluidcommunication with the at least one lumen, one or more sensorspositioned at or near a distal tip of the elongate tube, wherein the oneor more sensors are configured to measure a change in a parameter of theGRV indicators, and a controller in communication with the one or moresensors, wherein the controller is configured to determine a GRV basedon the change in the parameter of the GRV indicators.

In use generally, such an apparatus may be used to determine the GRV bypositioning the elongate tube defining at least one lumen therethroughinto the body lumen, introducing the medium having one or more GRVindicators through the at least one lumen and into the body lumen, andsensing the one or more GRV indicators via one or more sensorspositioned at or near a distal tip of the elongate tube. The one or moreGRV indicators may be monitored for a change in a parameter of the GRVindicators and the GRV of the stomach may be determined based on thechange in the parameter of the GRV indicators.

BRIEF DESCRIPTION OF THE DRAWINGS

Various exemplary embodiments are described in detail with reference tothe following figures, wherein:

FIGS. 1A-1C are schematics of an apparatus for placing a feeding tube inaccordance with an exemplary embodiment;

FIG. 2 is a flowchart of an exemplary method and apparatus for placing afeeding tube;

FIG. 3 is a schematic of a user interface screen of the exemplarymonitor of FIG. 1 ;

FIG. 4 is schematic of user interface screen of the exemplary monitor ofFIG. 1 ;

FIG. 5 is schematic of user interface screen of the exemplary monitor ofFIG. 1 ;

FIG. 6 is a schematic of an apparatus for placing a feeding tube inaccordance with another exemplary embodiment;

FIG. 7 is a schematic of an apparatus for placing a feeding tube inaccordance with another exemplary embodiment;

FIG. 8 is a schematic of an apparatus for assessing gastric motility inaccordance with an exemplary embodiment;

FIG. 9 is a schematic of an apparatus for measuring gastric residualvolume in accordance with an exemplary embodiment;

FIG. 10 is a flowchart of an exemplary method and apparatus formeasuring gastric residual volume;

FIG. 11 is a schematic of an apparatus for monitoring reflux inaccordance with an exemplary embodiment;

FIG. 12 is a flowchart of an exemplary method and apparatus formonitoring reflux;

FIG. 13 is a schematic of an exemplary conductive ink approach formeasuring impedance;

FIGS. 14A-14B are schematics of an exemplary tube connector;

FIG. 15 is schematic of a user interface screen of the exemplary monitorof FIG. 11 ;

FIG. 16 is schematic of a user interface screen of the exemplary monitorof FIG. 11 ;

FIG. 17 is a flowchart of an exemplary method and apparatus foralgorithms to determine presences of reflux;

FIG. 18 is a chart of impedance data indicating a liquid reflux event;

FIG. 19 is a chart of impedance data indicating a gas reflux event;

FIG. 20 is a chart of impedance data indicating a swallow event;

FIG. 21 is a chart of impedance data indicating a swallow and liquidreflux event;

FIGS. 22A-22E are schematics of an apparatus for measuring impedance andconductivity in accordance with exemplary embodiments;

FIG. 23 is a flowchart of an exemplary method and apparatus formeasuring GRV

FIG. 24 is a flowchart of an exemplary method and apparatus fordetermining the location a feeding tube via impedance measurements

FIG. 25 is a flowchart of an exemplary method and apparatus fordetermining the location a feeding tube via local conductivitymeasurements

FIG. 26 shows an embodiment of the GRV measuring device in a humanstomach.

FIG. 27 shows a stomach into which a substance containing aconcentration of a GRV indicator is introduced.

FIG. 28 shows a graph of the temperature of the stomach contents overtime as sensed by sensor(s) after a bolus of cold substance isintroduced into the stomach.

FIG. 29 shows a graph of the concentration or pH of a GRV indicator overtime after introduction into the stomach.

FIG. 30 shows a graph of the temperature of the stomach contents overtime as sensed by sensor(s) after multiple boluses of cold substance areintroduced into the stomach.

FIG. 31 shows an embodiment of the GRV measuring device where sensorsare outside of the stomach.

FIG. 32 shows an embodiment of the GRV measuring device where sensorsare located along the length of the catheter or tube.

FIGS. 33 and 34 show embodiments of the GRV measuring device wheresensor(s) are at different location.

FIG. 35 shows an embodiment of the GRV measuring device which isseparate from a feeding tube.

FIG. 36 shows a GRV measuring device where the GRV measuring device isinserted through a feeding tube.

FIGS. 37 and 38 illustrate how the sensor(s) of the GRV measuring devicemay be located at various places relative to the feeding tube.

FIG. 38 shows sensor(s) of the GRV measuring device in the pylorus

FIGS. 39-41 show embodiments of the invention in which there is at leastone transmitter and/or receiver to track location of the device withinthe stomach and/or stomach contents.

FIGS. 42 and 43 show embodiments of the GRV measuring device for usepercutaneously.

FIG. 44 shows an embodiment of the GRV measuring device for use with ajejunostomy tube.

FIGS. 45-49 show embodiments of the GRV measuring device.

FIG. 50 shows an embodiment of the device where GRV and entry in thestomach is based on a continuously or intermittently monitored physicalcharacteristic.

FIG. 51 shows an embodiment of the device.

FIG. 52 is a block diagram of a data processing system, which may beused with any embodiments of the invention.

FIGS. 53 and 54 show other embodiments of the GRV measuring device.

FIG. 55 shows the conductivity of various media when % gastric acid isincreased.

FIG. 56 shows pH and conductivity in various anatomical locations in apig.

FIGS. 57 and 58 show conductivity and oscillations of conductivity invarious locations in the anatomy before and after feeding.

FIGS. 59 and 60 show pH and oscillations of pH in various locations inthe anatomy.

FIG. 61 shows conductivity and pH before and after feeding.

FIG. 62 shows an embodiment of the GRV measuring device with retentionballoon.

FIG. 63 shows a GRV measuring device with a pH sensor.

FIG. 64 shows a GRV measuring device with a pH sensor.

FIG. 65 shows a cross section of a feeding tube of the GRV measuringdevice.

FIG. 66 shows an embodiment of the GRV measurement device.

FIG. 67 shows an embodiment of the GRV measurement device.

FIG. 68 shows an embodiment of the GRV measurement device.

DETAILED DESCRIPTION OF THE INVENTION

For convenience of explanation, exemplary embodiments are describedbelow with reference to the figures in the context of placing feedingtubes, assessing gastric motility, and monitoring reflux in acute carepatients.

A table of contents of some embodiments specifically disclosed in theDetailed Description is provided below.

I. Feeding Tube Location System and Apparatus

-   -   A. Determine Tube Location Using Acoustic Sensor    -   B. Determine Tube Location Using Magnetic Field Sensor

II. Motility Measurement System and Apparatus

-   -   A. Determine Motility Using Acoustic Sensor    -   B. Determine Gastric Residual Volume Using Temperature Sensor    -   C. Determine Gastric Residual Volume Using Bioelectrical        Impedance    -   D. Determine Motility Using Impedance Sensors

III. Reflux Measurement System and Apparatus

-   -   A. Reflux Measurement System    -   B. Feeding Tube Design    -   C. Monitor Cable Design    -   D. Suction and Feeding Pump Connector Design    -   E. Monitor Design

IV. Impedance Based Algorithms

-   -   A. Data Collection for Algorithms    -   B. Algorithms for Detecting Liquid Reflux    -   C. Algorithms for Detecting Gas Reflux or Belching    -   D. Algorithms for Detecting Swallows    -   E. Algorithms for Detecting Mixed Conditions    -   F. Algorithms for Smart Alarms

V. Aspiration Prevention Interventions

-   -   A. Aspiration Prevention Via Suction of Gastric Contents    -   B. Aspiration Prevention Via Adjustment of Feeding Pump    -   C. Aspiration Prevention Via Esophageal Obstruction

VI. Impedance Based Local GRV Measurement

VII. Tube Localization Through Impedance Measurements

VIII. Tube Localization Through Local Conductivity Measurements

The present disclosure now will be described more fully hereinafter withreference to the accompanying drawings, in which various embodiments areshown. The invention may, however, be embodied in many different formsand should not be construed as limited to the example embodiments setforth herein. These example embodiments are just that—examples—and manyimplementations and variations are possible that do not require thedetails provided herein. It should also be emphasized that thedisclosure provides details of alternative examples, but such listing ofalternatives is not exhaustive. Furthermore, any consistency of detailbetween various examples should not be interpreted as requiring suchdetail—it is impracticable to list every possible variation for everyfeature described herein. The language of the claims should bereferenced in determining the requirements of the invention.

In the drawings, the size and relative sizes of layers and regions maybe exaggerated for clarity. Like numbers refer to like elementsthroughout.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention. Asused herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. As used herein, the term “and/or” includes any and allcombinations of one or more of the associated listed items and may beabbreviated as “/”.

It will be understood that, although the terms first, second, third etc.may be used herein to describe various elements, components, regions,layers and/or sections, these elements, components, regions, layersand/or sections should not be limited by these terms. Unless the contextindicates otherwise, these terms are only used to distinguish oneelement, component, region, layer or section from another element,component, region, layer or section, for example as a naming convention.Thus, a first element, component, region, layer or section discussedbelow in one section of the specification can be termed a secondelement, component, region, layer or section in another section of thespecification or in the claims without departing from the teachings ofthe present invention. In addition, in certain cases, even if a term isnot described using “first,” “second,” etc., in the specification, itmay still be referred to as “first” or “second” in a claim in order todistinguish different claimed elements from each other.

It will be further understood that the terms “comprises” and/or“comprising,” or “includes” and/or “including” when used in thisspecification, are open-ended and specify the presence of statedfeatures, regions, integers, steps, operations, elements, and/orcomponents, but do not preclude the presence or addition of one or moreother features, regions, integers, steps, operations, elements,components, and/or groups thereof.

It will be understood that when an element is referred to as being“connected” or “coupled” to or “on” another element, it can be directlyconnected or coupled to or on the other element or intervening elementsmay be present. In contrast, when an element is referred to as being“directly connected” or “directly coupled” to another element, there areno intervening elements present. Other words used to describe therelationship between elements should be interpreted in a like fashion(e.g., “between” versus “directly between,” “adjacent” versus “directlyadjacent,” etc.). However, the term “contact,” as used herein refers todirect contact (i.e., touching) unless the context indicates otherwise.

Spatially relative terms, such as “beneath,” “below,” “lower,” “above,”“upper” and the like, may be used herein for ease of description todescribe one element's or feature's relationship to another element(s)or feature(s) as illustrated in the figures. It will be understood thatthe spatially relative terms are intended to encompass differentorientations of the device in use or operation in addition to theorientation depicted in the figures. For example, if the device in thefigures is turned over, elements described as “below” or “beneath” otherelements or features would then be oriented “above” the other elementsor features. Thus, the term “below” as used in a relative sense mayencompass both an orientation of above and below in the real world. Thedevice may be otherwise oriented (e.g., rotated 90 degrees or at otherorientations) and not affect the relationships described by thespatially relative descriptors.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which this disclosure belongs. It willbe further understood that terms, such as those defined in commonly useddictionaries, should be interpreted as having a meaning that isconsistent with their meaning in the context of the relevant art and/orthe present application, and will not be interpreted in an idealized oroverly formal sense unless expressly so defined herein.

I. Feeding Tube Location System and Apparatus

Determining the feeding tube location is important in a number ofclinical settings. For all patients who receive a feeding tube, it iscritical for the tube to be located in the stomach and not in the lungs.Feeding tubes inadvertently inserted into the trachea or lung airwaysoccurs in 0.3% to 15% of all insertions according to Thomas et al,“Confirmation of nasogastric tube placement by colorimetric indicatordetection of carbon dioxide: a preliminary report.” J Am Coll Nutr. 1998April; 17(2):195-7, hereafter “Thomas” which is hereby incorporated inits entirety herein by reference. Inserting a feeding tube into thelungs can cause a number of severe complications, such as lung tissueperforation and pneumonia. Described embodiments are designed to ensurethat the feeding tube is appropriately placed in the stomach and not inthe trachea, bronchi or lungs.

Proposed embodiments can be used with all types of feeding tubes,including the many different sizes (e.g., in a range of 6 Fr through 18Fr) and feeding tube forms, which can include, but is not limited to,Levin feeding tubes, Salem Sump style feeding tubes, Dobhoff feedingtubes, Keofeed feeding tubes, small bore feeding tubes, pediatricfeeding tubes, and nasojejunal feeding tubes.

A. Determine Tube Location Using Acoustic Sensor

An exemplary embodiment for determining tube location is to use a sensorto measure acoustic signals to determine where the tube is positioned inthe body. The acoustic sensor can measure different frequency ranges andtypes of vibrations including, but not limited to, vibrations associatedwith the frequency range of audible sounds (20-20,000 Hz). In anexemplary embodiment, a piezoelectric sensor is used to measure theacoustic signals. A number of other exemplary sensors can be used tomeasure acoustic signals, including but not limited to an electret,condenser, piezoelectric crystal, piezoelectric ceramic, piezoelectricfilm, fiber optic microphone, or contact accelerometers. FIGS. 1A-1Cshows an exemplary apparatus for a feeding tube with an acoustic sensor.In this exemplary embodiment, the patient utilizes a feeding tube 102 toreceive enteral nutrition into the stomach 103. The enteral nutrition isadministered by a feeding pump 116, which is conveyed via a feeding pumptube 114 and a tube connector 112. This feeding tube 102 contains anacoustic sensor 104. In an exemplary embodiment, this acoustic sensor104 is located on the distal tip of the tube. The acoustic sensor 104may be designed to detect certain vibrations, such as audible sounds,non-audible sounds or both audible and non-audible sounds. In anexemplary embodiment, the acoustic sensor 104 is connected via a wirethat is located in a second lumen that runs the length of the feedingtube 102. In some examples, the wire is embedded in the wall of thefeeding tube 102. In some examples, the acoustic sensor 104 and the wireare connected into a single and separate component that is placed insidethe main lumen of the feeding tube 102. This separate component is thenremoved after the tube insertion is completed by pulling the proximalend of the component. A hydrophilic coating can be applied in theinterior of the tube to reduce the friction in the interior and thusmake it easier to remove the component. A code or other uniqueidentifier can be integrated into the component and/or feeding tube 102such that the unique identifier is received by the monitor 110 andvalidated to ensure the same component and/or feeding tube 102 are notused for multiple patients. Use on multiple patients may not be safe orhygienic. In an exemplary embodiment, the code can be a series ofprinted alphanumeric characters or machine readable code (numeric and/ortext represented by a bar code or in near field communication device)ascribed to the component and/or feeding tube that is entered into themonitor, or controller, 110 for a validation step. In an alternativeembodiment, part of the component and/or feeding tube 102 can bedisabled upon removal of the component and/or electrical connector 106,making it infeasible to reuse the component and/or feeding tube inmultiple patients. In all of the previously described embodiments, awire can be connected to the electrical connector 106, which issubsequently connected to the monitor 110 via the cable 108. In analternative embodiment, the sensor can connect to the monitor via awireless interface, such as Wi-Fi, Bluetooth, cellular, or any otheradvantageous wireless network. It should be noted that use of the noun“monitor” herein refers to a computer, unless the context indicatesotherwise. Such a computer can be configured to track a patient'scondition, other data of a patient, medical instruments or equipmentused to assist a patient, etc. The monitor can preferably but optionallyinclude a display (e.g., monitor screen) or other indicator (e.g.,audible alarm) for a clinician. Although the disclosed embodiments referto a “monitor,” this usage should not be used to limit the invention.

This exemplary apparatus includes a sound emitter 118. The sound emitter118 is used to generate sounds that are then captured by the acousticsensor 104. The sound emitter 118 can utilize a piezoelectric transduceror other advantageous mechanisms to generate the desired sounds. “Sound”as used herein refers to any acoustic wave and is not limited to anaudible sound. Thus, the emitted sounds of the sound emitter 118 may beaudible or non-audible (or both). This sound emitter 118 is connected bythe wire 124 to the electrical connector 106. The sound emitter 118 canbe designed such that a standard ECG pad can be placed on the end of thesound emitter. Alternatively, the sound emitter 118 can be built into anECG pad, and thus can be connected to the wire 124 with the modified ECGclip. The sound emitter 118 may be placed close to the stomach. In anexemplary embodiment the sound emitter 118 may be placed on the abdomenjust caudal to the left costal margin.

In an exemplary embodiment, this apparatus also includes two electrodesensors. In this exemplary embodiment, the two electrode sensors areused to capture ECG data that can help the process of determining thelocation of the feeding tube. In this exemplary embodiment, electrodesensors 120-122 are connected to electrical connector 106 by wires126-128. The electrode sensors are used to record heart patterns andinterpret respiratory patterns. To determine heart patterns, theelectrodes detect the electrical activity of the heart. When theelectrical activity of the heart is displayed on an oscilloscope, adisplay of the monitor or paper chart, it is called an electrocardiogram(EKG or ECG). The respiratory pattern can be estimated from the ECGsignal, hereafter called the ECG respiratory pattern, by detecting therespiratory sinus arrhythmia (RSA), that is the modulation of the R-Rinterval (i.e., the time between consecutive ECG R-waves) during therespiratory cycle, as described by de Geus et al, “Ambulatorymeasurement of respiratory sinus arrhythmia and respiration rate.”Biological Psychology, vol. 41, no. 3, pp. 205-227, 1995, hereafter “deGeus” which is hereby incorporated in its entirety herein by reference.In an exemplary embodiment where another electrode is added to theapparatus, another option for estimating respiratory patterns from ECGsignals is enabled. Specifically, by examining the change of cardiacaxis during breathing that manifests itself as a change in QRSamplitude, according to Moody et al, “Derivation of respiratory signalsfrom multi-lead ECGs,” Computers in Cardiology, vol. 12, pp. 113-116,1985, hereafter “Moody” which is hereby incorporated in its entiretyherein by reference. In another exemplary embodiment, the respiratorypattern can be determined through impedance pneumography, In this case,an impedance between two electrodes is measured. The impedance increaseswith inspiration and decreases with expiration. The electrode sensors120-122 can be attached to the chest, arms, or other convenient oradvantageous locations. In an exemplary embodiment, the sound emitter118 can also serve the function of an electrode sensor. For example, thesame standard ECG pad may have both the sound emitter and ECG conductiveelectrode mounted thereon. Elements of the sound emitter and ECGconductive electrode may be shared. For example, the ECG conductiveelectrode may also function as a housing of the sound emitter. This canobviate the need for a second standalone electrode sensor in certaincircumstances. For example, utilizing the sound emitter 118 as anelectrode sensor can avoid the need for electrode sensor 122.

An exemplary process for utilizing the apparatus described in FIGS.1A-1C is provided in FIG. 2 . In the first step of this exemplaryprocess 201, the clinician enters patient data into the monitor (alsoreferred to herein as a controller) as shown in an exemplary depictionof a monitor screen shown in FIG. 3 . Patient data, such as name 302, IDnumber 304, sex 306, height 308 and weight 310, can be entered into themonitor manually or through an electronic data interchange. Optionally,the clinician can measure the distance between the nose, ear, and theumbilicus and enter the same into the monitor. In step 202, the monitor,based on this patient data, calculates and displays a target distance312 for inserting the tube. This target distance indicates the lengththe tube should be inserted into the patient (e.g., a distance measuredfrom the patient's front teeth, lips or nose) and can be visuallyverified by reference to measurement markings on the tube. The algorithmfor calculating the target measurement can be based on nomogram data asdescribed by Cirgin Ellett et al, “Predicting the Insertion Distance forPlacing Gastric Tubes.” Clin Nurs Res 2005 February; 14(1):11-27,hereafter “Cirgin Ellett” which is hereby incorporated in its entiretyherein by reference. The nomogram can be used to identify an appropriatetarget depth for tube insertion that is determined to correspond withcorrect placement of the end of the tube in the stomach of the patient.

An insertion message 314 is presented instructing the clinician to pausethe insertion once the tube has been inserted into the patient anintermediate distance (e.g., to a point where a specific distancemarking on the tube is about to pass into the nose or mouth). Inexample, this intermediate distance has been calculated as 25 cm. Thisintermediate distance can be determined by the computer as a function ofthe identified target depth for tube insertion (e.g., a ratio of theidentified target depth or by referencing a look-up table pairing arange of tube insertion depths to corresponding intermediate distances).This distance marking signifies the point where the clinician shouldpause the insertion to monitor for one or more signals consistent withthe tube being correctly inserted or consistent with the tube beingincorrectly inserted. The signals can be generated by the patient, suchas the sound of a heartbeat or the sound of breathing. In this example,the clinician can check the monitor to make sure that the tube is not inan inappropriate part of the airway, such as in the lower respiratorytract (i.e., past the glottis opening, or past the vocal folds, in thelarynx, in the trachea or in the bronchi) and/or that auscultated heartpattern is consistent with correct position. Data that indicate that thetube is correctly positioned in the esophagus might include one or moreof: 1) failure to detect the characteristic sounds of air moving in thelower respiratory tract, such as in the larynx, trachea and/or bronchi(“auscultated lower respiratory tract pattern”); 2) detection of thesounds made by the beating heart (“auscultated heart pattern”) within arange of appropriate intensities; 3) calculation of an appropriatedistance between the acoustic sensor and sound emitter.

In step 203, the clinician attaches the two electrodes 118, 120 to thebody, with 118 being ideally placed on the abdomen just caudal to theleft costal margin and 120 being placed in an accessible location suchas the shoulder. After attaching the two electrodes, the monitor willshow a message 316, if heart and respiration signals are being correctlyreceived and processed. Next, the clinician can proceed to step threeand press a button 318 at the start of tube placement, thus initiatingthe capturing and analyzing acoustic signals by the monitor. In thisexample, the monitor continually analyzes these acoustic signals todetect three separate patterns, specifically the auscultated lowerrespiratory tract pattern that is associated with being located in thelarynx, trachea and/or bronchi, the auscultated heart pattern, and thesound pattern from the sound emitter.

In step 204, the clinician begins to insert the feeding tube 102 intothe patient. As the feeding tube 102 is inserted, it is possible for thetube to enter the trachea 107, as shown in FIG. 1 a. As the tube isbeing inserted, the acoustic sensor 104 is capturing acoustic signalsand sending this data back to the monitor 110.

In step 205, the monitor 110 analyzes these acoustic signals todetermine if the signals indicate an auscultated lower respiratory tractpattern that is typically recorded when the acoustic sensor is locatedin the larynx, trachea 107 or a bronchus 109. The frequency of normallung sounds auscultated from outside of the body are in the range of 50to 2500 Hz according to Reichert et al, “Analysis of Respiratory Sounds:State of the Art.” Clin Med Circ Respirat Pulm Med. 2008 May 16;2:45-58, hereafter “Reichert” which is hereby incorporated in itsentirety herein by reference. Reichert also describes how trachealsounds can reach up to 4000 Hz. There are number of advantageousalgorithms and analysis techniques to determine if the acoustic signalsindicate auscultated lower respiratory tract patterns, including but notlimited to Fourier transform, wave-form, wavelet, and neural networksaccording to Earis et al, “Current methods used for computerizedrespiratory sound analysis.” Eur Respir Rev 2000; 10: 77, 586-590,hereafter “Earis” which is hereby incorporated in its entirety herein byreference. A Fourier transform approach to detecting and analyzingrespiratory sounds is described in Charbonneau et al, “Basic techniquesfor respiratory sound analysis.” Eur Respir Rev 2000; 10: 77, 625-635,hereafter “Charbonneau” which is hereby incorporated in its entiretyherein by reference. In step 205, the monitor also analyzes the ECGsignals to determine an ECG respiratory pattern, which can beaccomplished via the previously described exemplary approaches ofdetecting the RSA or changes in QRS amplitude.

In an exemplary embodiment the monitor may perform an analysis to matchthe initially detected auscultated respiratory pattern with the ECGrespiratory pattern that is derived from the electrodes, as shown instep 206. In an exemplary embodiment, this comparison can provideadditional information that can help ensure that an auscultatedrespiratory pattern has been detected in the sound detected by theacoustic sensor. There are a number of exemplary approaches to determineif there is a match between the auscultated and ECG respiratorypatterns. In an exemplary embodiment, the monitor performs an analysisto match the key or identifiable points in the auscultated respirationpattern with the key or identifiable points in the ECG respirationpattern. These key or identifiable points can be derived from specificaspects of inhalation and exhalation related to respiration and thetiming of such key or identifiable points. For example, a key oridentifiable point can be the timing of the peak of the auscultatedlower respiratory tract pattern and the timing of the peak of the ECGrespiration pattern. Similarly, the timing of the trough of theauscultated respiration pattern and the timing of the trough of the ECGrespiration pattern can be used as a key or identifiable point. In anexemplary embodiment, one respiration pattern can be used as a startingpoint to determine if the other respiration pattern is a match. Forexample, by continually measuring the ECG respiration pattern, it ispossible to generate a baseline of key or identifiable points of therespiration pattern and then analyze the auscultated respiration patternto determine the corresponding existence of these key or identifiablepoints, or to analyze just these key or identifiable points to determineif there is a match or correlation of sufficient magnitude. This patternmatching can include one or more of data smoothing, time seriesanalysis, cross-correlation analysis, convolution analysis, regressionanalysis, and neural networks. Matching the two patterns can beadvantageous, since the auscultated respiration pattern is more likelyto be a valid respiration pattern indicative of being located in thelarynx, trachea or bronchi when the auscultated respiration patternmatches the continually measured ECG respiration pattern derived fromthe ECG signal. If the two patterns (i.e., the ECG respiratory patternand the auscultated respiratory pattern) match or correlate to asufficient degree, then it is highly likely that the acoustic sensor islocated in the lower respiratory tract, such as the larynx, trachea or abronchus.

The results of this respiratory pattern analysis are presented on themonitor as shown in step 207. If the results are negative, the monitordisplays the message that the feeding tube is not located in the tracheaor a bronchus. If an auscultated lower respiratory tract pattern isdetected (e.g., a match or significant correlation with the ECGrespiratory pattern is detected), the monitor can indicate a visualalarm, and/or an auditory alarm, to warn the clinician that the tube maybe located within the lower respiratory tract, such as the larynx,trachea or a bronchus. The clinician can then stop tube insertion andwithdraw the tube.

In step 208, the acoustic sensor detects the auscultated heart patternas the feeding tube is being inserted. The auscultated heart pattern canbe detected immediately upon tube insertion in the body since the heartcan emit a strong signal, i.e., a signal that is loud and can travelsignificant distances within the body. The spectrum for capturing theauscultated heart pattern is generally defined as between 20 and 100 Hzaccording to Reichart. There are a number of advantageous means toanalyze heart sounds to determine the auscultated heart patternincluding but not limited to Fourier transform and wavelet transformaccording to Debbal et al, “Computerized heart sounds analysis.” ComputBiol Med. 2008 February; 38(2):263-80. Epub 207 November 26, hereafter“Debbal” which is hereby incorporated in its entirety herein byreference.

If the monitor detects an auscultated heart pattern, in an exemplaryembodiment the monitor will then perform an analysis to match theauscultated heart pattern with the ECG heart pattern that is derivedfrom the electrodes, as shown in step 209. In this exemplary embodiment,this comparison can provide additional information that can help ensurethat an auscultated heart pattern has been detected. A number ofprocessing steps can be required to perform this pattern matching,including but not limited to data smoothing, time series analysis,cross-correlation analysis, convolution analysis, regression analysis,and neural networks. Matching the two patterns is advantageous, sincethe detected heart sound pattern is more likely to be an actual heartsound pattern when the pattern matches the continually measured andwell-known ECG-based heart pattern derived from the electrodes. Matchingthese two patterns therefore increases the confidence that the acousticsensor is correctly detecting the heart pattern.

As shown in FIG. 1 b, as the clinician inserts the feeding tube 102 downthe esophagus 101, the acoustic sensor 104 moves within close proximityof the heart 111. The monitor 110 is continually measuring the intensityof the heart sound as the feeding tube 102 transits the length of theesophagus 101 as it moves toward the stomach 103. As the feeding tube102 gets closer to the heart 111 during this transit, the heart soundshould increase in intensity, or amplitude. Conversely, as the feedingtube 102 moves past the heart 111 and gets close to entering the stomach103, the heart sound should decrease in intensity, or amplitude. Thisincreasing and decreasing intensity in the measured auscultated heartpattern can be analyzed to determine an approximate location of thefeeding tube, e.g., a location of the feeding tube's relative to theheart of the patient. The measurement of the auscultated heart patternwill be analyzed over time to determine if it matches a similarincreasing and decreasing pattern of intensity, as shown in step 210. Anumber of processing steps can be required to perform this patternmatching, including but not limited to data smoothing, time seriesanalysis, cross-correlation analysis, convolution analysis, regressionanalysis, and neural networks. For example, the maximum amplitude of theauscultated heart pattern can be identified and plotted versus time.These points can then be analyzed to confirm a substantially continuousrise of the amplitudes to the maximum amplitude and/or confirm asubstantially continuous decline from the maximum amplitude. In step211, the results of this analysis are shown on the monitor, such as amessage describing the status of the analysis and a chart showing theintensity of the auscultated heart pattern over time.

In step 212, the monitor analyzes the acoustic signals coming from thesound emitter 118 and captured by the acoustic sensor 104, andcalculates the distance between the sound emitter and acoustic sensor.The acoustic signal can take many exemplary forms, including but notlimited to a sound pulse, a continuous variable tone and can be emittedat different audible, ultrasound, or other advantageous frequencies. Byknowing the precise timing of initiating the acoustic signal from thesound emitter and the timing of receiving the signal by the acousticsensor, the monitor can perform calculations to determine the distancebetween the sound emitter and the acoustic sensor. For example, when apulse is emitted at time t1 by the sound emitter 118 and received attime t2 by the acoustic sensor 104, in an exemplary embodiment, thedistance x can be calculated as x=(t1−t2) x v, where v=the speed ofsound through the patient (v can be determined through calibration,i.e., tested on the patient from known distances, or determined fromempirical data). This process therefore provides the distance betweenthe acoustic sensor 104 and the sound emitter 118. In step 213, themonitor displays the status of the distance calculation and a chartshowing these distance calculations over time. In some embodiments, themonitor may display a distance that is derived from the distance betweenthe acoustic sensor 104 and the sound emitter 118 (e.g., a distanceremaining to complete insertion of the feeding tube).

In an exemplary embodiment, the clinician pauses the insertion to checkthe monitor after inserting the tube approximately halfway into thepatient, such as in FIG. 1 b. The purpose of checking the monitor is todetermine if any of the summary data would indicate the tube is locatedin the trachea or bronchi, or if the tube appears to be locatedcorrectly in the esophagus, as shown step 214. In this example, theclinician pauses the insertion based on tube markings close to the pointof entry, such as the nose or mouth, indicating the tube had beeninserted 25 cm. Other exemplary markings and insertion distances mayapply, such as those having a dependence on or calculated based upon theidentified target depth or otherwise calculated as a function of thedata of the patient (such as size, age, sex, etc.). The clinician cancheck the monitor to see if there is any indication the tube tip islocated in the larynx, trachea or bronchi. The clinician can also checkthe monitor to see if the auscultated heart pattern has increased inintensity, which would be an indication that tube has progressed downthe esophagus and is near the heart. The combination of no indicatedauscultated lower respiratory tract pattern along with an increase inintensity of an auscultated heart pattern indicates that the tube isprogressing correctly down the esophagus towards the stomach. Theclinician can also check the monitor to see if the calculated distancebetween the acoustic sensor and the sound emitter has decreased duringthe period of insertion. This decreasing distance indicates that tubehas progressed down the esophagus, and conversely has not become coiledin the mouth, nasopharynx or hypopharynx. The combination of noauscultated lower respiratory tract pattern, an increase in intensity ofan auscultated heart pattern, and decreasing distance between theacoustic sensor and the sound emitter provide a strong indication thatthe tube is progressing correctly down the esophagus towards thestomach. Any combination of an indication of an auscultated lowerrespiratory tract pattern, an indication that the auscultated heartpattern intensity has not increased with insertion of the tube, and noevidence of decreasing distance between the acoustic sensor and thesound emitter, may indicate the tube is not progressing correctly downthe esophagus towards the stomach and may be in the trachea or bronchior has become coiled. After reviewing these data, the clinician can thendecide whether to proceed with the tube insertion or take other action,such as removing and reinserting the feeding tube or taking an X-ray toconfirm the placement of the tube.

In FIG. 1 c, the acoustic sensor 104 is shown in the stomach 103 andlocated more closely to the sound emitter 118. After the clinician hasinserted the tube 102 to the recommended insertion distance, theclinician can check the monitor to see the distance between the soundemitter 118 and the acoustic sensor 104. The clinician can then comparethis calculated distance with a visual identification of seeing wherethe sound emitter 118 is physically placed on the patient and making anassessment as to whether the distance corresponds with the feeding tube102 being correctly placed in the stomach 103 and conversely not in thetrachea or bronchi 109. As the feeding tube 102 progresses toward andinto the stomach 103, the calculated distance between the sound emitter118 and acoustics sensor 104 should decrease.

In step 215, the clinician reviews the summary information and inputsthe distance marking on the tube into the monitor. This distance markingcorresponds with the furthest point the tube has been inserted into thepatient. The monitor then compares the inputted tube distance with therecommend insertion distance calculated in step 202. If the differencebetween the two insertion distances is above a defined threshold, themonitor will display a message that the tube insertion distance may notbe sufficient for proper location in the stomach. If the differencebetween the two insertion distances is below a defined threshold, themonitor will display a message that the tube insertion distance issufficient. In an exemplary embodiment, the threshold for the differencein tube distance is 5 cm; in another embodiment, the threshold for thedifference is 10% of the identified target depth.

FIG. 4 depicts an example monitor screen where all assessments haveindicated that the tube is placed correctly in the stomach. The mostvisible indication on the screen is the status indicator 401, whichdisplays the color green to signify the tube is placed correctly. If themonitor algorithm calculations result in an indication that the tube isnot placed correctly, or if there is not enough information to determineif the tube is placed correctly, the status indicator 401 displays thecolor yellow. If the monitor algorithm calculations result in anindication that the tube is placed in the trachea or a bronchus, thestatus indicator 401 displays the color red. In addition, a text statusindicator 402 conveys the status of the tube placement. In the scenariofor FIG. 4 , the text status indicator indicates the “Tube PlacedCorrectly”. The heart and respiratory signal indicator 403 displays amessage, “Heart and Respiratory Connected”, signaling that the heart andrespiratory signals from the electrodes are being correctly captured.The trachea and lung sounds signal indicator 404, displays a message,“No Trachea/Lung Sounds Detected”, signaling that the acoustic sensorand monitor are currently not detecting any trachea or lung sounds, andthus indicating the feeding tube tip is not in the trachea or bronchus.The heart transit indicator 405, displays a message, “Tip Passed Heartin Esophagus”, signaling that the acoustic sensor and monitor detectedthe pattern of the tube tip passing by the heart during transit down theesophagus. The indication of the tube tip passing by the heart duringtransit down the esophagus is further confirmation that the tube tip isnot located in the trachea or bronchus. The sound emitter distanceindicator 406, displays a message, “Tip 3 Cm from Sound Emitter”,signaling the acoustic sensor is located 3 cm from the sound emitter.The indication that the acoustic sensor is located a short distance fromthe sound emitter, which should be located caudal to the left costalmargin, is further confirmation that the tube tip is located in thestomach, and conversely is not located in the trachea or bronchus. Thetube insertion indicator 407 displays a message, “Tube Insertion of 45cm Is Sufficient”, signaling that the inputted tube insertion distanceis sufficient for the tube to be placed correctly in the stomach. If theclinician is satisfied that the data presented on the monitor issufficient to confirm the tube is correctly placed in the stomach, theclinician can then submit the electronic medical record by pressingbutton 409.

The clinician also has the option to review more detailed data on themonitor. By pressing the Data Chart View button 408, the clinician canview more detailed information in chart form. FIG. 5 shows this optionalview to review the data in chart form. For example, the clinician canreview the Heart Sound Intensity chart 501 to see a time-based view ofthe heart sound intensity data. If the feeding tube transited theesophagus correctly, this would be indicated by an increase inauscultated heart pattern intensity as the tube tip gets closer to theheart and a decrease in intensity as it passes the heart on the waytowards the stomach. The clinician can also view feeding tube tipdistance 502 over time (e.g., graphically), which should generallyindicate a decrease in tube tip distance from the sound emitter as thetube is being inserted. Alternatively, the clinician may review theheart sound intensity with respect to the measured feeding tube tipdistance. In this example, the measured feeding tube tip distance may beplotted along the x-axis and the heart sound intensity may be plottedalong the y-axis. The clinician may repetitively sample the heart soundintensity at the same distances by inserting and retracting the feedingtube.

After the tube has been inserted, the clinician can still refer to themonitor to see an update of the distance between the acoustic sensor andthe sound emitter. This may be valuable to determine if the tube hasmoved during treatment and if the tube insertion may need to beadjusted.

In an exemplary embodiment, the clinician can utilize the same monitorfor multiple patients. In this embodiment, the monitor associates aunique ID with each feeding tube. If the feeding tube was disconnectedfrom the monitor and subsequently reconnected, the monitor can utilizethe unique ID of the feeding tube to associate all previously enteredand measured data from that feeding. Therefore, a clinician can utilizeone monitor to insert feeding tubes into multiple patients, and asnecessary reconnect the monitor to a tube to assess the location of thetube without having to reenter any patient data. A history of patientdata is stored such that any previously entered patient data can also beaccessed and associated with any new feeding tubes.

FIG. 6 shows an alternative embodiment of the apparatus to determinefeeding tube location. In this exemplary embodiment, two sound emitters601 and 602 are used to determine the distance from the acoustic sensor104 to the sound emitters. The sound emitters 601 and 602 are connectedto a rigid member 603. The rigid member 603 is connected via wire 604 toelectrical connector 106. The two sound emitters 601 and 602 also serveas electrodes to capture heart and respiratory signals. The distancebetween the acoustic sensor 104 and the sound emitters 601 and 602 thatcan be calculated in the same fashion as described elsewhere herein.Therefore, in each instance in time, the distance between acousticsensor 104 and sound emitter 601 is known and the distance betweenacoustic sensor 104 and sound emitter 602 is known. Additionally, thedistance between sound emitter 601 and sound emitter 602 is known giventheir fixed location on the rigid member 603. These three distances forma triangle, so knowing the lengths of each side of the triangle makes itpossible to calculate the angles of this triangle and thus determine thelocation of the acoustic sensor. With one sound emitter (e.g., just oneof 601 and 602), you can determine the location of the acoustic sensoras being a certain distance away from the one acoustic sensor (e.g.,determined to be on a point of the surface of an imaginarythree-dimensional sphere having the location of the one acoustic sensoras its center). In this exemplary embodiment with two sound emitters,you can determine the location of the acoustic sensor as being on apoint of the circumference of an imaginary two-dimensional circle 605.This level of accuracy in determining the location of the acousticsensor 104 may be advantageous. For example, when the two sound emitters601 and 602 are arranged vertically, the imaginary circle on which theacoustic sensor 104 is determined to lie will be horizontal. Thus, avertical location of the acoustic sensor 104 can be accuratelydetermined even if its horizontal location has been determined via thiscalculation to be on the horizontal imaginary circle. Using three soundemitters (not shown in FIG. 6 ) that are arranged in a triangle andspaced apart known distances (i.e., not linearly arranged) allows forfurther precision in determining the location of the acoustic sensor.Triangulation can be used to calculate a point in space relative to thelocation of the three sound emitters. For example, for each of the threesound emitters, a sphere with the corresponding sound emitter as itscenter can be determined, with the radius of the sphere representing thedetermined distance between the sound emitter and the acoustic sensorand the surface of the sphere representing a possible location of theacoustic sensor. The intersection of these three determined spheres canbe determined as the location of the acoustic sensor. Another approachis to use each pair of the three sound emitters to calculate possiblelocations along a corresponding imaginary circle. The intersection ofthese three imaginary circles will correspond to a determined locationof the acoustic sensor 104.

FIG. 7 shows an alternative embodiment of the apparatus to determinefeeding tube location. In this exemplary embodiment, the apparatusutilizes a mobile device 701 (shown as 701 a, 701 b and 701 c atrespective different locations). This mobile device 701 can take theform of a mobile phone, tablet, or other advantageous mobile device. Inthis embodiment, the mobile device 701 uses a wireless connection tocommunicate with the monitor 110. A tip component 707 is located in thetip of the feeding tube and, in this embodiment, is used to sense theacoustic signals from the mobile device 701. In an exemplary embodiment,the mobile device 701 continuously emits a acoustic signal. In thisembodiment, the tip component 707 is the acoustic sensor 104. The signalreceived by the tip component 707 is used by the monitor 110 tocalculate the distance between the tip component 707 and the mobiledevice 701.

An exemplary process is to move the mobile device 701 while the tipcomponent 707 receives the sound signals. In a first position, mobiledevice 701 a is a calculated first distance from tip component 707 wherethe distance can be visualized as the radius of a first sphere 702 (withmobile device 701 a at the center) and the location of the tip component707 is somewhere on the surface of that first sphere 702. In a secondposition, mobile device 701 b is a calculated second distance from tipcomponent 707 where the distance can be visualized as the radius of asecond sphere 703 (with mobile device 701 b at the center) and thelocation of the tip component 707 is somewhere on the surface of thatsecond sphere 703. In a third position, mobile device 701 c is acalculated third distance from tip component 707 where the distance canbe visualized as the radius of a third sphere 704 (with mobile device701 c at the center) and the location of the tip component 707 issomewhere on the surface of that third sphere 704. If you assume theacoustic sensor is not moving between the three positions then theintersection point 705 where each of the three spheres intersects is thelocation of the tip component 707 in three-dimensional space.Determining location via this process is called trilateration, asdescribed by Wikipedia, “Trilateration”. Wikipedia. Web. 3 Mar. 2015.Web. <http://en.wikipedia.org/wiki/Trilateration>. To determine thisintersection point 705, you need to first determine the location of themobile device 701 in each position relative to the other positions.

In an exemplary embodiment, the location of each position relative tothe other positions can be determined by utilizing an accelerometer andgyroscope contained in the mobile device 701. The accelerometer andgyroscope can enable calculating the position, orientation and velocityof the mobile device and thus enable determining a relative location ateach time interval. In an exemplary embodiment, the mobile device emitssound signals at 20 Hz, or 20 times per second, and thereforecontinually calculates relative location 20 times per second. Otherexemplary frequencies for emitting a sound signal and calculatingrelative location can be used.

In an exemplary embodiment, the accuracy of determining the relativelocation of the mobile device 701 can be enhanced by using an additionalreference point. In an exemplary embodiment, a known visual reference706 can be utilized. In this embodiment, a camera contained in themobile device 701 can be utilized to view the visual reference 706. Anexemplary form for this visual reference 706 can be a two dimensionalrectangle with a length of 2 cm on one side and 4cm on the other sideattached to the body of the patient. Another exemplary form for thisvisual reference 706 can be a high contrast, two dimensional marker ofknown dimensions which lacks reflection symmetry and/or rotationsymmetry attached to the body of the patient. Other forms and dimensionscan be used. Since the form and dimensions are known, algorithms in thesound emitter 701 can analyze data from the camera to calculate thedistance from the visual reference 706 to the mobile device 701 based onthe characteristics of the visual reference 706, such as calculateddiameter of the disk compared to the known diameter and the shape of thedisk compared to the known shape.

In an exemplary embodiment, the relative position of tip component 707can be communicated to the clinician via an augmented reality interfaceon a screen contained in the mobile device 701. Augmented reality isdefined as viewing data in what appears to be a camera field of view. Inthis embodiment, the clinician can look at the screen of the mobiledevice 701 and see what appears to be a real-time video feed of thepatient. The clinician can first wave the mobile device 701 forward,then backward, and from side to side over the patient to calculate arelative location of the tip component 707. The clinician can then seeon the screen of the mobile device 701 a representation of the tipcomponent 707 on the screen relative to its position within thepatient's body. The visual representation of the patient's body on thescreen can exhibit a transparency effect to create the illusion that youcan see the tip component 707 within the patient's body. An exemplaryembodiment of this transparency effect can be within the sight line ofthe tip component 707, the patient's body has an algorithm generatedsurface appearance that makes it look as if you're looking beneath thesurface of the patient's body. The clinician should therefore be able tosee the location of the tip component 707 relative to the patient'sanatomy and determine if the tip component 707 is correctly placed inthe stomach, and conversely is not placed in the trachea or bronchus. Inan exemplary embodiment, an algorithm-generated appearance can alsosimulate a visual representation of organs such as the stomach, lungsand heart to assist the clinician and determining the location of theacoustic sensor.

B. Determine Tube Location Using Magnetic Field Sensor

In an exemplary embodiment, an alternative (or additional) apparatus canbe used in a similar process previously described for the mobile device701 and the tip component 707. This alternative (or additional)apparatus comprises a magnetic field sensor, or magnetometer, containedwithin the mobile device 701. The magnetometer can measure the strengthof the magnetic field that is around the mobile device 701. In anexemplary embodiment, the tip component 707 can contain magneticmaterial with a known magnetic moment. In an alternative embodiment, thetip component 707 consists of coiled wiring that upon application of aknown electric signal creates a known magnetic moment. In an exemplaryembodiment, the clinician can also wave the mobile device 701 forward,then backward, and from side to side over the patient. Instead ofmeasuring distance between the mobile device 701 and the tip component707 based on the elapsed time for the sound signal to travel betweenthem, the distance is instead calculated based on the strength of themagnetic field measured from the magnetic material in the tip component707. The measurement of distance (measured in meters) from the mobiledevice 701 in the tip component 707 can be calculated using thefollowing exemplary formula:

$d = \sqrt[3]{\frac{\mu_{0}}{4\pi}\frac{2\mu}{B}}$

In this formula μ₀ represents the permeability constant (4π×10−7 T m/A),μ is the magnetic moment of the magnetic material in the tip component707, and B is the magnetic field (measured in tesla). The clinician cansimilarly be able to view an augmented reality visual representation ofthe tip component 707 relative to the patient's body on the screen ofthe mobile device 701. In an exemplary embodiment, the accuracy ofdetermining the relative location of the mobile device 701 can also beenhanced by using a known visual reference 706, as previously described.

II. Motility Measurement System and Apparatus

Determining if the patient is tolerating enteral nutrition is criticallyimportant in delivering effective care and avoiding devastatingcomplications. Determining whether the patient has satisfactory gastricmotility can indicate if enteral nutrition will be tolerated. Normalgastric motility can be defined as periodic or occasional peristalticmovements of the stomach that propel the contents of the stomach intothe small intestine. FIG. 8 shows an example of this peristalticmovement. In FIG. 8 , a peristaltic wave 801 is shown moving through thestomach 103. These peristaltic waves 801 move the food through thestomach 103 and out through the pyloric sphincter 803 into the duodenum804 according to Ehrlein et al, “Gastrointestinal Motility.” ClassTutorial, Technische Universität München, 2014, hereafter “Ehrlein”which is hereby incorporated in its entirety herein by reference. Duringthe movement of a peristaltic wave 801, muscles in the stomach 103contract to push food 802 from the proximal stomach 103 towards thepylorus 803 at the distal end of the stomach. In addition to peristalticwaves 801, the stomach 103 moves food 802 towards the pylorus 803 bygenerally contracting and thus shrinking the size of the overall stomach103; this phenomenon is called tonic contraction. The peristaltic waves801 and tonic contraction encourage the food 802 to be further brokendown and thus digested. Food that is broken down to a point where it ismore of a liquid is referred to as gastric chyme 805. The peristalticwaves 801 more easily move this gastric chyme 805 past the pylorus 803and into the duodenum 804, and conversely larger undigested pieces offood 802 are pushed back into the stomach 103 to be further digested inan effect called retropulsion. Understanding gastric motility can behelpful to the clinician in many ways. First, if the patient appears tohave good motility, there is less risk the patient may reflux gastriccontents into their lungs. Second, good motility may indicate theclinician can accelerate the level of nutrition for the patient, whichwould potentially assist with recovery. Certain embodiments provideadvantageous means for measuring motility.

A. Determine Motility Using Acoustic Sensor

In an exemplary embodiment, an acoustic sensor is used to measuregastric motility. This acoustic sensor 104 can be located on the distaltip of the feeding tube 102, as shown in FIG. 8 . This acoustic sensor104 can measure different frequency ranges and types of vibrationsincluding, but not limited to, vibrations associated with frequencyrange of audible sounds (20-20,000 Hz). In an exemplary embodiment, apiezoelectric sensor is used to measure the acoustic signals. A numberof other exemplary sensors can be used to measure acoustic signals,including but not limited to an electret, condenser, piezoelectriccrystal, piezoelectric ceramic, piezoelectric film, or contactaccelerometers. The vibrations measured by the acoustic sensor 104 canoriginate from a number of sources, including but not limited toperistalsis, gas bubbles, flatulence, and sounds from nearby organs,such as the lungs, heart, or small bowel. The study of phonoenterographyrevealed that bowel sounds increased in intensity during a meal and highintensity persisted for more than two hours after the meal according toWatson et al, “Phonoenterography: the recording and analysis of bowelsounds.” Gut. 1967 February; 8(1): 88-94, hereafter “Watson” which ishereby incorporated in its entirety herein by reference. Bowel soundsare complex with a mixture of tones and often in a sequence of closelyconnected sounds in a frequency range of 150 to 5,000 Hz.

A number of sources of vibration may be detected. In a study by Campbellet al, “Surface vibration analysis (SVA): a new non-invasive monitor ofgastrointestinal activity.” Gut, 1989 January; 30(1):39-45, (hereafter“Campbell” which is hereby incorporated in its entirety herein byreference) Campbell attempted to quantify these bowel sounds andmeasured vibrations in the 40-10,000 Hz frequency range with apiezoelectric sensor. Specific patterns of bowel sounds can beassociated with the fasting state and the postprandial state associatedwith the food being digested and thus monitored to determine the same.

In one embodiment, an acoustic sensor detects the vibrations associatedwith the movement of a peristaltic wave. In this exemplary embodiment,the acoustic sensor 104 can be a piezoelectric-based accelerometer. Inaddition (or in the alternative), the accelerometer is capable ofmeasuring movement (e.g., physical movement of the accelerometeritself), such as the peristaltic wave 801 that moves down the stomach103. For example, the peristaltic wave 801 can be detected by detectinga pattern having a frequency of one to three contractions per minute, asshown in FIG. 8 .

A positive indication of gastric motility (e.g., between 1 and 3contractions/waves per minute) should correlate with the patienttolerating enteral nutrition, and therefore have sufficient sensitivity.In contrast, a negative indication of motility (e.g., less than 1contractions/waves per minute) can help identify patients that are nottolerating nutrition, enabling the clinician to adjust care and monitorthe patient more closely.

To ensure that the acoustic sensor 104 is functioning correctly, themonitor can routinely monitor other body sounds as a means to check ifthe apparatus is functioning correctly. In an exemplary embodiment, themonitor routinely captures an auscultated heart pattern. If theauscultated heart pattern is routinely captured correctly, thisindicates the acoustic sensor is functioning correctly, and thus it canbe inferred it is also correctly capturing gastric motility vibrationmeasurements. In an alternative embodiment, the monitor can routinelycapture acoustic signals from the sound emitter 118 to confirm theacoustic sensor 104 is functioning correctly.

In an exemplary embodiment, an acoustic sensor measures the vibrationsassociated with oscillating gas bubbles in the small intestine. In thisexemplary embodiment, the acoustic sensor 104 can be apiezoelectric-based accelerometer. There is evidence these gas bubblesare continually present in the small intestine according to Liu et al.“Oscillating Gas Bubbles as the Origin of Bowel Sounds: A CombinedAcoustic and Imaging Study.” Chin J Physiol. 2010 Aug. 31; 53(4):245-53hereafter “Liu” which is hereby incorporated in its entirety herein byreference. Bubbles can be identified by their oscillating frequencies.Further, the size of the bubbles can also be determined by the measuredfrequency. The size of the bubbles can change as they move within thedifferent sized structures of the small intestine. In one embodiment,the pattern and frequency of the bubbles is analyzed to assessgastrointestinal motility and other gastric functions. The analysis ofgas bubbles in the small intestine can be combined with the analysis ofperistaltic waves in the gastric environment, or other sensor data, toassess overall gastrointestinal motility.

In an exemplary embodiment, the various gastric motility measurementscan additionally be used to determine the effectiveness of the type andamount of enteral nutrition. In an exemplary embodiment, the patientcondition can also be a factor in determining the effectiveness of thetype and amount of enteral nutrition. By collecting data on the patientcondition, the type and amount of enteral nutrition and/or the resultingmeasurement of gastric motility, it may be possible to guide the typeand amount of enteral nutrition and/or obtain the optimal gastricmotility for each patient condition. Conversely, analyzing these datacan provide insights on which enteral nutrition types and amounts shouldnot be used for specific patient conditions.

B. Determine Gastric Residual Volume Using Temperature Sensor

It is standard of care in hospitals to measure the volume of the gastriccontents of patients receiving enteral nutrition. This procedure isreferred to as measuring Gastric Residual Volume (GRV). Gastric residualvolume is typically measured by attaching a large syringe to theproximal opening in the feeding tube and suctioning all of the gastriccontents into the syringe. The syringe has measurement markings denotingthe volume in milliliters, which is then recorded in the patient'smedical record. A low volume of gastric contents may indicate thepatient is tolerating enteral nutrition and has sufficient gastricmotility. A high-volume of gastric contents may indicate the patient isnot tolerating enteral nutrition and does not have sufficient gastricmotility. A high-volume of gastric contents is defined as 250 mLaccording to McClave et al, “Guidelines for the provision and assessmentof nutrition support therapy in the adult critically ill patient.” JPENJ Parenter Enteral Nutr. 2009 May-June; 33(3):277-316, hereafter“McClave” which is hereby incorporated in its entirety herein byreference. A clinician can adjust the care of the patient based onreceiving a high gastric residual volume measurement, such as reducingthe rate of tube feeding, prescribing pro-kinetic agents or raising thehead of bed. However, a high gastric residual volume may not alwayscorrespond to a gastric motility problem. In some cases, a gastricresidual volume of over 250 mL may be required to trigger gastricemptying by the stomach into the small intestine, and thus a gastricresidual volume of over 250 mL may be part of normal digestion. Inaddition, these gastric residual measurement calculations are oftenperformed every four hours in acute care patients receiving enteralnutrition. This procedure therefore takes time away from the cliniciansthat otherwise can be used in treating patients. The procedure is alsooften unsanitary due to the removal and reinsertion of gastric contents.

In an exemplary embodiment, an indicator dilution technique is used tomeasure GRV. Indicator dilution techniques are well known and are widelyused in medicine, scientific work and industry for measuring fluid (gasor liquid) volumes or flow rates. As described by Schoeller “IndicatorDilution Methods.” Quality of the Body Cell Mass. Serono Symposia USA2000, pp 55-67, hereafter “Schoeller” which is hereby incorporated inits entirety herein by reference, indicator dilution methods formeasuring volume (or flow rate) are based on the principle ofconservation of mass. The addition of a known quantity of tracer(indicator) to the pool of tracee yields, after equilibration, asolution wherein the final concentration of indicator is equal to theamount of indicator added divided by the pool volume. If volume is thedesired read-out, then the equation is re-arranged: volume (poolsize)=dose of tracer/concentration of tracer.

The validity of indicator dilution approach depends on four assumptions.First, the indicator mixes rapidly and thoroughly with the fluid in thepool. Second, after mixing is complete, the concentration of theindicator is homogeneous in the pool volume. Third, the indicator isdistributed only to the pool volume of interest. Fourth, the tracer isstable (over the time period required for the measurements).

Although these assumptions are often valid in vitro, when indicatordilution techniques are applied in vivo (such as, for medicalapplications) some or even all of the assumptions typically are notsatisfied perfectly. Thus, for medical (or other in vivo biological)applications, indicator dilution methods are rarely perfectly accurate.Nevertheless, these approaches are often accurate enough to beclinically useful. Moreover, as will be discussed below, it may bepossible to partially adjust for systematic errors in measurement byincorporating empirically derived coefficients into the final equationsthat are employed for converting the measured signal into clinicallyuseful information.

Indicators often are chemicals that can be easily detected, usingappropriate analytical means. Examples include: radio-labelled compounds(e.g., tritium-labelled water), stable isotope-labelled compounds (e.g.,13C-labelled glucose), dyes (e.g., indocyanine green dye), or easilydetected chemical entities (e.g., Li+ cation, polyethylene glycol).

GRV has been measured, using an indicator dilution approach. In thelaboratory, a model stomach showed that dilution of phenol red dye canbe employed to determine “gastric” volume according to Hurwitz,“Measuring gastric volume by dye dilution.” Gut 1981 February;22(2):85-93, hereafter “Hurwitz” which is hereby incorporated in itsentirety herein by reference. Subsequently, GRV measurement in patientswas demonstrated using polyethylene glycol (PEG) as the tracer andturbidometry as the means for measuring PEG concentrations according toHardy et al, “Determining gastric contents during general anaesthesia:evaluation of two methods.” Can J Anaesth. 1987 September; 34(5):474-7,hereafter “Hardy” which is hereby incorporated in its entirety herein byreference. These authors showed that GRV measured using the indicatordilution technique was not significantly different from the GRV measuredby aspiration (via a Levin nasogastric tube) of the gastric contents.

Temperature also can be a useful tracer. For example, cardiac output(i.e., the flow rate of blood through the heart) is commonly measured inclinical practice by injecting a known quantity of cold normal salinesolution into the venous side of the circulation and detecting theresulting change in blood temperature in the pulmonary artery. In anexemplary embodiment, gastric residual volume is determined by measuringthe temperature of gastric contents before and after a control. In thisembodiment, a temperature sensor is located on the distal tip of thefeeding tube, which can be connected via a wire to the monitor. Themonitor 110 can take continuous temperature measurements of the gastriccontents. The apparatus is similar to that shown in FIG. 8 , but insteadof an acoustic sensor 104 located the distal tip, a temperature sensoror thermistor is used. Of course, a combination of multiple sensors canbe used, such as those sensors disclosed herein and other sensors, andsuch combinations should be considered within the scope of thisinvention. The monitor can then control a known amount of fluid to beintroduced through the feeding tube and into the stomach, which in anexemplary embodiment can be 50 mL of distilled water cooled to atemperature of 1° C. Utilizing water as a control can be advantageous,since acute care patients require hydration and water is a safesubstance. The temperature sensor can then continually measure thechange in temperature of the gastric contents after introducing thiscontrol of cooled water. In an exemplary embodiment, the GRV can becalculated using the following equation:

GRV=k ₁ ×k ₂ ×V _(injectate)(T _(before) −T _(injectate))/(T _(before)−T _(after))

In this equation, V_(injectate) is the volume of cold water injectedinto the stomach via the feeding tube. T_(before) is the temperature ofthe gastric contents prior to injecting the aliquot of cold water.T_(injectate) is the temperature of the cold injectate. T_(after) is thetemperature of the gastric contents after the injection of theindicator. k₁ is a dimensionless constant that depends on the specificheat content of water, the density of water, the specific heat contentof gastric contents and the density of gastric contents. k₂ is adimensionless constant that accounts for the dead space volume of thefeeding tube and perhaps other unmeasured sources of systematic error.In an exemplary embodiment, the rate in which the temperature changeoccurs throughout the gastric contents can be used to calculate GRV.Calculating the rate of change of the temperature can add information toimprove the calculation of GRV or provide other insights that may provehelpful to the clinician. The nature of the stomach environment and thegastric contents are such that significant mixing occurs as part ofdigestion and the subsequent measured temperature change will bereflective of the entirety of the gastric contents. Other factors thatcan be used to calculate GRV include the rate of enteral nutrition, therate of gastric emptying, and medicines that may be introduced into thegastric environment. Since there may be unaccounted-for factors that mayinfluence the accuracy of the gastric residual volume calculation, thealgorithm can also present a probability measurement associated with thevolume calculation to help the clinician understand the relativecertainty in the GRV calculation.

C. Determine Gastric Residual Volume Using Bioelectrical Impedance

In an alternative embodiment, Gastric Residual Volume can be determinedin certain circumstances by measuring changes in the impedance of analternating current applied in the abdominal region by electrodesaccording to Soulsby et al, “Measurements of gastric emptying duringcontinuous nasogastric infusion of liquid feed: electric impedancetomography versus gamma scintigraphy.” Clin Nutr. 2006 August;25(4):671-80, hereafter “Soulsby” which is hereby incorporated in itsentirety herein by reference. In the approach described by Soulsby, 16electrodes (ECG pads) are applied in a circumferential pattern aroundthe abdomen. Impedance changes are measured by passing a sinusoidalalternating current (50-100 kHz; 1 to 10 mA) between one pair ofelectrodes on the abdomen and measuring the resulting voltage dropbetween another pair of electrodes. In the approach described bySoulsby, impedance is measured from all the possible combinations ofpairs of electrodes, and an impedance versus time curve is generated bya proprietary algorithm. The system is “calibrated” by introducing a 100mL bolus of tube feeding into the stomach. The conductivity of thecalibrating bolus of tube feeding formula is increased by dissolving 17g/100 mL of table salt (NaCl) in the formula prior to introducing itinto the stomach.

A similar approach to Soulsby is described by McClelland et al,“Epigastric impedance: a non-invasive method for the assessment ofgastric emptying and motility.” Gut. 1985 June; 26(6):607-14, hereafter“McClelland” which is hereby incorporated in its entirety herein byreference. There is also a similar approach described by Sutton et al,“Measurement of gastric emptying rates by radioactive isotope scanningand epigastric impedance.” Lancet. 1985 Apr. 20; 1(8434):898-900,hereafter “Sutton” which is hereby incorporated in its entirety hereinby reference. The approach described by McClelland and Sutton is similarto the one described above, except that only four electrodes areemployed (two on the anterior epigastrium and two on correspondinglocations on the back). The system described by McClelland and Suttonuses “standard” impedance cardiography equipment for signal generationand detection, but employs appropriate low-pass filtering to excludeinterference from cardiac signals. In the approach described byMcClelland and Sutton, gastric volume is not measured; rather, theimpedance based system is designed only to measure fractional changes ingastric volume after a test meal as a function of time. Thus, theprimary read-out is the half-time (t_(1/2)) for gastric emptying.

In one embodiment, a GRV monitoring device can employ the electrodeplacement strategy described by McClelland and Sutton, as shown in FIG.9 . In an exemplary embodiment, a plurality of electrodes are placed onthe abdomen. Here, four electrodes 118, 120, 902 and 904 are placed onthe abdomen. An alternating electric current is driven through thepatient's body between electrodes 118 and 902. The voltage betweenelectrodes 120 and 904 may also be measured. The voltage measurement isfiltered to only reflect the changes within the frequency range of thealternating current between electrodes 118 and 902. The voltagemeasurement comprises an impedance measurement whose amplitude dependsin part on the GRV. Electrodes can have plural functions. For example,electrode 118 can record ECG signals during tube placement and serve asan anterior electrode that inputs alternating current for subsequentimpedance measurement. Electrode 118 can be placed in the angle betweenthe left costal margin (of the rib cage) and xyphoid process of thesternum (breast bone). Similarly, the electrode 120 can record ECGsignals and also serve as an anterior electrode for measuring voltagefor impedance measurement. Electrode 120 can be placed just caudal tothe left costal margin at location that is about 4 finger-breadths(about 4-5 cm) to left of the midline. In this embodiment, electrode 902can be placed on the posterior of the patient and input alternatingcurrent for subsequent impedance measurement. Electrode 904 can also beplaced on the posterior of the patient and measures voltage along withelectrode 120 for impedance measurement. In another embodiment, the sameelectrode placement strategy can be employed, except instead of placinga pair of electrodes on the posterior, these electrodes instead can belocated on the distal end of the feeding tube and connected by wires (orconductive ink) to an appropriate fitting on the proximal end of thetube. In this exemplary embodiment, electrode 120 on the anteriorabdominal wall and electrode 910 on the feeding tube can input, or“inject”, an alternating current (50-100 kHz; 1 to 10 mA) into thepatient. Each of the second electrode 912 on the distal end of thefeeding tube and electrode 118 on the anterior abdominal wall canreceive an alternating current from each of electrodes 120 and 910.Detecting the voltage and current between two of the electrodes, theimpedance of the gastric contents plus other relevant tissues (e.g.,fat, muscle, and skin) between the two electrodes can be determined. Inan exemplary embodiment, the patient is electrically isolated from theexternal environment during this procedure.

An exemplary process for utilizing the apparatus described in FIG. 10 tomeasure GRV via impedance is provided in FIG. 10 . In the first step ofthis exemplary process 1001, the clinician installs electrodes on theabdomen and inserts the feeding tube. In step 1002, the nutrition typeand infusion rate is entered into the monitor 110. In step 1003, theclinician confirms that the patient is prescribed acid suppressionmedication via the monitor 110. In step 1004, the system is calibratedby first emptying the stomach completely (by aspiration of contents viathe feeding tube). Impedance is then measured with GRV=0. Then, a knownquantity (e.g., 50 mL) of the prescribed tube feeding formula isinjected into the stomach via the feeding tube and impedance measuredagain (e.g., with GRV=50 mL). For more accuracy, three-point calibrationcan be achieved by injecting a second bolus of tube feeding formula(e.g., another 50 mL aliquot) and again recording impedance. In step1005, impedance measurement is initiated via the monitor 110. In step1006, nutrition is initiated via the feeding pump 116. GRV measurementis then displayed on the monitor 110 per step 1007. In step 1008, inaudible and/or visual alarm is initiated if the GRV exceeds a definedthreshold. This defined threshold of GRV measurement can be customizedvia a setup configuration of the monitor 110, and may include a defaultconfiguration based on patient sex, height, weight, feed type, fluidrestriction, propofol rate, etc. In step 1009, the monitor 110 candisplay whether peristalsis has been detected or not. Knowing ifperistalsis has been detected can help the clinician determine ifnutrition is being tolerated. Peristalsis can be detected throughdescribed embodiments or other advantageous means. In step 1010, aprobability is calculated to determine if the GRV measurement is beingcaptured and analyzed correctly. This probability will be based on anumber of factors, including but not limited to the GRV measurementvalue, the trending of GRV measurement values, nutrition type andinfusion rate, prescription of acid suppression medication, calibrationresults, and peristalsis detection. The results of this probabilitycalculation can be displayed on monitor 110. In step 1011, the clinicianmay decide to perform an optional additional calibration. In thisoptional calibration, the impedance measurement is noted via the monitor110. The stomach is then emptied completely by aspiration of contentsvia the feeding tube. The clinician then manually measures the volume ofthe aspirated gastric contents. The clinician then enters the manuallymeasured volume of the gastric contents into the monitor 110. Themonitor 110 then utilizes the manually measured volume to calibrate theGRV measurements going forward. In step 1012, the GRV measurementresults are entered into the EMR system.

In an exemplary embodiment, a conductivity sensor can be located at thedistal end of the feeding tube. In an exemplary embodiment, theconductivity sensor can take the form of electrode 910. The conductivitysensor can be utilized to determine the conductivity (inverse ofresistivity) of the gastric contents. This conductance measurement canbe helpful for estimation of GRV, since the estimation of GRV usingmeasurements of epigastric impedance (see FIG. 10 ) depends onconductivity of the gastric contents and the other structures (e.g.,skin, muscle tissue, adipose tissue) and their volumes in the epigastricregion being interrogated by the impedance measurement electrodes. Thestomach contains relatively conductive material and when GRV increases,the measured impedance decreases. An increase in the conductivity of thegastric contents will also cause a drop in the measured impedance. Bymeasuring the conductivity, this confounding variable can be factoredout from the estimation of GRV. By extension, the measurement of GRV viaimpedance depends on a difference in impedance of the gastric contentsand these other structures (e.g., skin, muscle tissue, adipose tissue).If the ionic strength of the tube feeding formula is too low, then thedifference in impedance between the gastric contents and the otherstructures in the epigastric region of interest will be insufficient toprovide a reliable signal for estimating GRV. In the researchlaboratory, this problem can be solved in a simple way by adding a largequantity (e.g., 9 g/L; 154 mEq/L) of sodium chloride (NaCl; table salt)to the standard tube feeding formula to ensure that the ionic strengthof the tube feeding formula is sufficient to provide a good impedancesignal for estimation of GRV. In the clinical setting, however, it wouldbe ill-advised to add large quantities of sodium chloride to the tubefeeding formulas that are administered to patients, since many patientscannot tolerate large loads of either sodium ion (Na+) or chloride ion(Cl−). Some commercial tube feeding formulas contain high concentrationsof Na+ and potassium ions (K+), and therefore have sufficient ionicstrength to permit reliable estimates of GRV, using the epigastricimpedance methodology. One such formula is Osmolite 1.2, which contains58 mEq/L of Na+ and 46 mEq/L of K+. Other commercial tube feedingformulas contain relatively low concentrations of Na+ and K+, andtherefore may not have enough ionic strength to permit reliableestimates of GRV, using the epigastric impedance methodology. An exampleof this type of tube feeding formula is Nutrihep, which contains 7 mEq/Lof Na+ and 33 mEq/L of K+. The ionic strength (and, hence, theconductivity) of the gastric contents is determined not only by theionic composition of the tube feeding formula, but also by the secretionof ions (H+, K+, Cl−) by the gastric mucosa into the lumen of thestomach. Thus, in order to determine whether the contents of stomach atany given point in time have a composition that is suitable fordetermination of GRV would be desirable to continuously monitor theconductivity of the gastric contents. Moreover, since calibration of theepigastric impedance monitoring system (by injecting into the stomach aknown volume of tube feeding formula) will be done only intermittentlyand the rate and composition of gastric secretion of ions can change ona minute to minute basis, it would be useful to adjust the GRVcalibration settings continuously by taking into consideration measuredchanges (relative to the value measured at the time of calibration) ofthe conductivity of the gastric contents.

D. Determine Motility Using Impedance Sensors

In an exemplary embodiment, impedance sensors like those described inthis disclosure to measure reflux in the esophagus, can be used in thestomach to measure the patient's motility. In one embodiment, thismeasurement can function the same way as impedance sensors in theesophagus. While in the stomach, food and gastric secretions that spantwo sensors typically have a lower impedance measurement than if nofood/secretions were spanning the sensors. Measuring the pattern ofimpedance that results from food coming into the stomach and draininginto the small intestine can create data that can be interpreted as ameasurement of motility. The timing, duration, sequencing, and othermeasurements from the impedance sensors can be interpreted andcorrelated with either normal or potentially abnormal motility. In anexemplary embodiment, the measurements from the impedance sensors can becorrelated with the peristalsis waves within the stomach that are anormal function of digestion. This information can be used by theclinician to modify the nutrition delivery or potentially trigger othertypes of care. In the case where an algorithm determines there isabnormal motility, the level of nutrition can be automatically reducedto prevent the risk of aspiration. In another example, abnormal motilitycan trigger suction of gastric contents.

This impedance sensor data in the stomach can also be combined withsensor data in the esophagus, so the combination of motility data andreflux data, can then automatically reduce the feeding level, trigger analarm, trigger suction, trigger a balloon, or actuate other features.Conversely, the sensor data can trigger an increase of the feeding levelif proven algorithms determine that the patient has good motility, noreflux, and is tolerating the nutrition well.

III. Reflux Measurement System and Apparatus

Some embodiments are directed to methods and apparatus for addressing areflux event in an esophagus. More particularly, some embodiments aredirected to determining initiation of a reflux event, and takingremedial measures.

A. Reflux Measurement System

An exemplary apparatus for monitoring reflux and providing someprotection from aspiration is shown in FIG. 11 . In this exemplaryembodiment, the patient utilizes a feeding tube 102 to receive enteralnutrition into the stomach 103. The enteral nutrition is administered bya feeding pump 116, which is conveyed via a feeding pump tube 114 and atube connector 112. This feeding tube 102 contains impedance sensors1101-1108 that are positioned on the outside of the tube 102 and alongthe tube section that is located in the esophagus 101. In an exemplaryembodiment, there are eight impedance sensors 1101-1108 that comprise aconductive electrode in order to measure the impedance between twodifferent sensors. When reflux material spans two sensors, theelectrical impedance between the two sensors is reduced. This differencein measured impedance is captured by the monitor 110 via a cable 108 andelectrical connector 106 that connects the impedance sensors 1101-1108on the feeding tube 102 to the monitor 110. In specific circumstances,it can be determined that the patient is at risk for immediateaspiration, so in an exemplary embodiment the gastric contents aresuctioned to prevent the gastric contents from being aspirated. In thisembodiment, suctioning is accomplished via a suction tube 1109 that isconnected to the feeding tube 102 via a tube connector 112. The suctiontube 1109 is connected to wall suction 1110, which passes throughmonitor 110. Monitor 110 contains a valve that controls the level ofsuction from wall suction 1110 that is applied to suction tube 1109.

An exemplary process for utilizing the apparatus described in FIG. 11 isprovided in FIG. 12 . The first step of this exemplary process 1201 isto insert the feeding tube 102 into the patient. This can beaccomplished via the standard methods for inserting feeding tubes. Instep 1202 the feeding tube 102 is connected to the monitor via cable108, to wall suction 1110 via suction tube 1109 and tube connector 112,and to the feeding pump 116 via the feeding pump tube 114. In step 1203,the feeding pump 116 is initiated and enteral nutrition starts to flowthrough the feeding pump tube 114 into the feeding tube 102 via the tubeconnector 112. In step 1204, the monitor 110 continually measuresimpedance data from the impedance sensors 1101-1108 on the feeding tube102. In step 1205, the monitor 110 continually analyzes the changes inthe impedance data to determine if the changes correlate to patternsthat may indicate reflux or swallows. In step 1206, suction can beinitiated if a pattern is recognized for reflux. This suction isinitiated by monitor 110 opening a valve that enables wall suction 1110through suction tube 1109 and feeding tube 102 via the tube connector112.

B. Feeding Tube Design

An exemplary embodiment for the device that captures data in the refluxmonitoring system is a feeding tube. In this embodiment, the feedingtube can be any relevant feeding tube used in acute care or deliveringenteral nutrition to patients. In one exemplary embodiment, the feedingtube is of size 14 Fr., which has an outer diameter 4.7 mm. Otherexemplary embodiments can include other feeding tube sizes, which caninclude, but is not limited to 10 Fr., 16 Fr., and 18 Fr. In anexemplary embodiment, the tube is in the form of a Levin Feeding Tube.This is a non-sterile standard Levin type feeding tube for nasogastricor orogastric insertion. Other exemplary embodiments can include otherfeeding tube forms, which can include, but is not limited to, Salem Sumpstyle feeding tubes, Dobhoff feeding tubes, Keofeed feeding tubes, smallbore feeding tubes, pediatric feeding tubes, and nasojejunal feedingtubes. In one exemplary embodiment, the feeding tube is 48 inches (122cm) long. Other exemplary embodiments can include other feeding tubelengths.

In an exemplary embodiment, the feeding tube is made of polyurethane. Inanother exemplary embodiment, the feeding tube is made of PVC. Inanother exemplary embodiment, the feeding tube is made of silicon. Otherexemplary embodiments can include other feeding tube materials.

In an exemplary embodiment, the feeding tube has holes in the distal tipof the tube to allow enteral nutrition to enter the gastric environment,or enable suction to remove gastric contents. These holes can be of adifferent number, sizes and shapes and can additionally include a holein the tip of the feeding tube.

In an exemplary embodiment, the tube includes radio opaque material toconfirm placement in the stomach 103 and esophagus 101 with an X-ray. Inan exemplary embodiment, radiopaque markings can be placed at 30 cm, 40cm, 50 cm and 60 cm from distal end. Other exemplary embodiments caninclude other placements of radiopaque markings or radiopaque materialcan be included in the tube material. In an exemplary embodiment,radiopaque material can be placed along the length of the feeding tube,and potentially be integrated into the feeding tube via the tubeextrusion process. In another exemplary embodiment, the impedancesensors can potentially serve as the radiopaque markings. Otherradiopaque materials and placements can be used. These radiopaquemarkings can be used in combination with other techniques to determinetube placement. For example, if the nomogram recommends a depth of 50 cmfrom the nose, and the tube is inserted to this distance, the likelihoodis higher that the plain film X-ray will show the feeding tube to be inthe correct position. It is desirable for the impedance sensors to beradio-opaque enough to be visible on a plain X-ray film, e.g. regularchest X-ray. In general, correct position is defined as all impedancesensors being located in the thoracic region of the esophagus, i.e. thesensor closest to the feet is above (superior to) the stomach.

In an exemplary embodiment, it may be desirable for half the sensors tobe above the carina (a clear landmark on chest X-ray) and the other halfof the sensors to be below (inferior to) the carina but still above thediaphragm. A potentially accurate method of measuring the extent ofreflux is measuring based on the location of the carina. This apparatusand method allows for reporting of the height of reflux events relativeto a fixed part of the body, e.g. the carina, rather than relative tothe feeding tube. In this exemplary embodiment, the feeding tube hasradio-opaque markers that are numbered or otherwise distinguishable fromone another. For example, the most distal sensor (closest to the feet)can be 1 bar. The next sensor can be 2 bars, so on and so forth, untilthe most proximal (the 6^(th) sensor) can be 6 bars. After insertion tothe recommended depth (using an acoustic sensor, nomogram, or any othermethod) a plain X-ray may be taken. Description of the acoustic sensorand its use described elsewhere herein may be implemented as all or partof sensor 1111. The monitor then asks the user to input the number ofbars for the impedance sensor that is closest to and below the carina.The carina may be a preferred reference point since it is both easilyidentified by most clinicians and it is located approximately in themidpoint of the thoracic, so it represents the point approximately halfway up the esophagus. Once the sensor information is inputted (as above)the monitor can then report whether reflux is occurring “below” or“above” the carina. Therefore, instead of (or in addition to) reportingheight of reflux relative to the feeding tube, e.g. 10 cm, the reportingof height is relative to the approximate midpoint of the esophagus, withhigher reflux, i.e. superior to the carina, being more extensive.

An alternative embodiment for confirming the location of a feeding tubeis to measure the tube insertion relative to the location of the LowerEsophageal Sphincter (LES). In an exemplary embodiment, a small balloonis integrated into the feeding tube. This is similar to an endotrachealtube in concept. After inserting the feeding tube into the stomach, oneinflates a high volume (e.g. 100 ml) low-pressure balloon at or near thedistal end of the tube. After inflation with 100 mL of air using astandard syringe, one gently pulls the tube out until there is pressureresulting from the balloon hitting the LES. It may be desirable for theballoon to be 10 or 15 cm from the tip of the feeding tube such thatwhen resistance is met, the tube is taped in place, and one knows thatthe tip of the feeding tube is in the stomach to allow foradministration of tube feeds and medications into the stomach. Usingthis approach, it would be desirable for the most distal (closest totip) impedance sensors to be located 5-10 cm from the area of theballoon that is closest to the head. At the conclusion of placement ofthe feeding tube, the balloon is deflated (i.e. air removed) and thefeeding tube is taped, bridled, or otherwise affixed to the nose in theexample of nasal insertion. This method and apparatus may accuratelylocate the LES, and more particularly, a length of the passage from thepoint of tube insertion (e.g., mouth or nose) to the LES. The approachmay alleviate the need to confirm tube placement with an X-ray since thefeedback of knowing the tube is located proximal to the LES may alsoconfirm it is not in the lungs or curled up in the stomach given theknown length of the tube proximal to the balloon.

In an exemplary embodiment, the tube includes tube length markings orother indicia to indicate a length of the tube from its distal tip andthus be used by the clinician to determine a length of a tube insertedinto the patient. For example, the tube length markings may start at 25cm from the distal tip to 85 cm in 5 cm increments. These tube lengthmarkings will allow the clinician to determine how much of the feedingtube has been inserted into the patient. Other exemplary embodiments caninclude other tube length markings.

Exemplary feeding tubes may utilize sensors to measure potential refluxin patients. In one exemplary embodiment, impedance sensors may beutilized, which generally contain sensor material that is conductive inorder to measure the impedance between two different sensors. In oneexample, a bolus 1112 of stomach contents moves up the esophagus 101 ina retrograde movement, as shown in in FIG. 11 , and simultaneously comesinto contact with multiple impedance sensors 1102, 1103 and 1104. Theimpedance between each adjacent pair of impedance sensors may becontinually measured. In an exemplary embodiment, this continuousmeasurement is at a frequency of 50 Hz. Other advantageous frequenciescan be used in the successful operation of the product. When bolus 1112spans two sensors, 1102 and 1103, the electrical impedance between thetwo sensors, 1102 and 1103, is reduced. This measurement of theimpedance between two sensors may be referred to as measuring theimpedance of a channel. Additionally in this example, the bolus 1112spans sensors 1103 and 1104, reducing the impedance in this additionalchannel. In an exemplary embodiment, the impedance sensors 1101-1108 arespaced 2 cm apart. Other exemplary embodiments can include other sensorspace locations. In an exemplary embodiment, the feeding tube 102 willcontain six channels and thus eight impedance sensors locatedapproximately 25 cm to 50 cm from the distal tip, such as being locatedat 30 cm for sensor 1101, 32 cm for sensor 1102, 34 cm for sensor 1103,36 cm for sensor 1104, 41 cm for sensor 1105, 43 cm for sensor 1106, 45cm for sensor 1107 and 47 cm for sensor 1108, from the distal tip. Theselocations assume the gastro-esophageal junction, also the location ofthe LES, is located approximately 25 cm from the distal tip. Otherexemplary embodiments can include other total number of impedancesensors and other locations of sensors.

In one exemplary embodiment, sensor 1111 may be implemented as a pHsensor 1111 that is located on or adjacent the distal tip of the feedingtube at 0 cm location, as shown in FIG. 11 , or at a location 0 cm to 5cm or 0 cm to 15 cm. The pH sensor 1111 may be used to measure the pH ofthe gastric contents. In an exemplary embodiment, this pH sensor 1111 isused in conjunction with a drug to determine if a patient may tolerateenteral nutrition. In this embodiment, the feeding tube may measure thepH change before and after administration of the drug.

The pH sensor 1111 can be placed in other locations along the feedingtube. One exemplary embodiment is to place a pH sensor 1111 atapproximately 25 cm from the distal tip and to use the sensor to measurepH and help determine if there is reflux present. This pH informationcan augment the impedance information or be used independently. In anexemplary embodiment, if pH drops at the same time the impedance sensorsmeasure a drop in impedance, the pH drop can be considered additionalconfirming evidence there is reflux Additionally, the pH sensor 1111 canprovide the pH of the potential reflux helping to determine the relativeacidity of the reflux. The level of acidity can be used in determiningthe appropriate level of care. For example, reflux at a low pH can bemore damaging to the esophagus and lungs, so specific care can beinitiated, such as prescribing acid suppressants, prescribingpro-kinetic agents, or further raising the head-of-bed.

In an exemplary embodiment, the pH sensor 1111 will conform to thefollowing specifications. The pH sensor material consists of antimony.The pH sensor 1111 may measure and display pH to at least one decimalplace, i.e. x.x. The sensor accuracy (offset) of the initial pHmeasurement may have a margin of error of +/−0.3. Subsequent pHmeasurements may have precision of +/−0.1. The pH sensor 1111 can havean internal reference for ease of use. The pH sensor 1111 may have auseful life of 3 days.

In one exemplary embodiment, the impedance sensors can take the form ofmetal rings that are to be applied to the feeding tube to measureimpedance between the metal rings. An exemplary material for thesesensors can be stainless steel, but other exemplary metal materials canbe used that satisfy the impedance measurement requirements. Impedancesensors utilizing metal rings, and specifically stainless steel, mayhave a similar design, for example, as those provided with the SandhillScientific ZepHr catheters that are used to measure reflux to assist inthe diagnosis of Gastro-Esophageal Reflux Disease (GERD) (seehttp://www.sandhillsci.com/index.php?activePage=reflux&page=zprobes) buthave a size to wrap around a feeding tube that is sized 10-18 Fr.

In an exemplary embodiment, metal rings are integrated into the feedingtube 102 to measure impedance in patients that are receiving enteralnutrition. An exemplary embodiment for integrating metal rings can be tocreate the feeding tube with two lumens. The main lumen is utilized todeliver food to the stomach and to apply suction to remove stomachcontents. A second lumen is utilized to route wires that will connect tothe metal rings to help complete an impedance measurement circuit. Inthis embodiment, the metal rings are attached by bending around theoutside of the feeding tube, staying in place by either friction,bonding via an adhesive material, or some exemplary combination. Thesemetal rings can substantially cover the circumference of the feedingtube, partially cover the circumference or cover the entirecircumference. In this embodiment, each wire that is drawn through thelumen is drawn through a hole in the feeding tube at each location of ametal ring and soldered to the metal ring. Exemplary embodiments caninclude various sizes, shapes, and different locations in the lumen tosufficiently connect the metal rings.

In an exemplary embodiment, the proximal end of the feeding tube has anelectrical connector that connects the wires in the second lumen to acable that will enable connectivity to a controller or a monitor. Theelectrical connector can connect these wires in many different ways.

In an exemplary embodiment, an electrical connector 106 will connect thewires attached to the sensors 1101-1108 to a cable 108 that will connectwith a monitor 110. In an exemplary embodiment, this cable 108 is 2 m inlength, although other exemplary lengths can be used. In an exemplaryembodiment, this cable 108 has an RJ-45 connector at the end that willconnect to the monitor 110, although other exemplary connectors can beused.

In an exemplary embodiment, conductive ink is utilized as the sensors1101-1108 instead of metallic rings, as shown in FIG. 13 . In anexemplary embodiment, the wires 1301-1308 that connect to the sensors1101-1108 may instead be formed of a conductive ink. Many differenttypes of conductive ink can enable effectively collecting this data. Inan exemplary embodiment, the conductive ink used is AGCL-675Silver/Silver Chloride Ink provided by a company called ConductiveCompounds. In these embodiments, the conductive ink is printed orotherwise applied directly to the surface of the feeding tube. In oneexemplary embodiment, the conductive ink wires 1301-1308 and sensors1101-1108 are applied by a printing process to thin films 1310-1311. Theconductive ink can be applied in other exemplary processes such as apad, pen, inkjet, laser, screen print, nano-based processes and otherprocesses that may prove advantageous. An exemplary pattern for printingthe conductive ink wires 1301-1308 and sensors 1101-1108 is in a designthat does not allow the wires or the sensors to overlap on the printedthin films 1310-1311 surface. An exemplary design can be made ofdifferent layers of ink and dielectric. One exemplary embodiment is toprint these different layers as part of a printing process. An exemplaryprocess for printing is to first print a dielectric material in apattern that matches the wiring pattern. In this exemplary process, nodielectric is printed where the design specifies sensors 1101-1108. Inthis exemplary process, the conductive ink wires 1301-1308 are printedon top of the dielectric pattern. In this exemplary process, the sensors1101-1108 are then printed on the thin films 1310-1311 in such a way asto be in contact with the conductive ink wires 1301-1308. In thisexemplary process, an adhesive material is then printed on top of thewires 1301-1308 and sensors 1101-1108.

In an exemplary process, the conductive ink wires 1301-1308 and sensors1101-1108 are applied to the feeding tube 102 via a combination ofpressure and heat. In this exemplary process, specific tooling iscreated for the size of tube 102 where the conductive ink is applied.The conductive ink film 1310-1311 and tube 102 are placed in the toolingand then heat is applied to activate the adhesive material. The toolingalso applies pressure to press the conductive ink onto the tube 102.After this process, the film 1310-1311 is removed from the tube 102,leaving only the printed conductive ink and dielectric materialremaining on the tube 102. The resulting tube 102 includes a pluralityof sensors 1101-1108 adhered to the tube and exposed to the externalthrough openings in the dielectric material to the environment. Each ofthe plurality of sensors 1101-1108 are connected to a corresponding oneof the conductive ink wires 1301-1308, also adhered to the outer surfaceof the tube but insulated from the external environment from thedielectric material.

The size and shape of the conductive ink sensors can take many exemplaryforms. In one exemplary embodiment, the sensors 1101-1108 are in theform of a rectangle that covers a portion of the circumference of thetube 102, as shown in FIG. 13 . Other exemplary shapes can be used, suchas a square, oval, circle, etc. Per FIG. 13 , an exemplary approach toconnecting the sensors 1101-1108 to the monitor 110 is via conductiveink wires 1301-1308 that transverse the tube from the sensors 1101-1108to an electrical connector 106. An exemplary pattern for the conductiveink wires 1301-1308 is to run parallel to the length of the film1310-1311 and connect to the sensors 1101-1108 via a right angle. Theremay be other exemplary patterns for efficiently printing the conductiveink wires 1301-1308 to each sensor 1101-1108. An exemplary thickness ofthe conductive ink wires is about 0.020 inches, but other thicknessescan be used.

The size and shape of the films 1310-1311 the conductive ink wires1301-1308 and sensors 1101-1108 are printed on and the number of sensors1101-1108 printed can vary depending on the size of the tube 102, thelocation of the sensors 1101-1108 to capture sensor data, and the numberof sensors 1101-1108 required to capture the data. An exemplary size andshape is shown in FIG. 13 , where two conductive ink films 1310-1311 canbe utilized to capture the required sensor data. In this exemplaryembodiment, the tube 102 to which the conductive films 1310-1311 areapplied is a 14 Fr. Levin tube that is 4.67 mm ( 3/16 inch) outerdiameter and 122 cm (48 inches) long. In this exemplary embodiment, eachof the films 1310-1311 can cover an arc of 120 degrees when placed onthe 14 Fr. tube 102, equating to a film width of 4.92 mm (0.193 inches).The length of the first film 1310 can be 50 cm (19.66 inches), and thelength of the second film 1311 can be 62 cm (24.41 inches). Each filmcan contain 4 impedance sensors, which enables three channels of sensordata collection since two adjacent sensors can form a channel.

The positioning of each film 1310-1311 depends on factors such as tubelength and the area to be monitored. In this exemplary embodiment, theproximal end of both films 1310-1311 can be placed starting at 90 cmfrom the distal tip of the feeding tube. In this exemplary embodiment,each film 1310-1311 can be positioned 180 degrees with respect to theother, so they effectively cover opposite sides of the tube. Thisembodiment should enable effectively capturing the data and positioningthe films 1310-1311 optimally for ease of production.

In this embodiment, the first sensor 1101 can be positionedapproximately 30 cm from the distal tip. This position should beadvantageous since the lower esophageal sphincter is locatedapproximately 25 cm from the distal tip. Therefore, reflux is measuredstarting at 5 cm above the lower esophageal sphincter. As a comparison,the clinical diagnosis of GERD is reflux reaching 5 cm above the loweresophageal sphincter. In this embodiment, each impedance sensor islocated approximately 2 cm from the other.

At the proximal end of the tube 102 near where the thin films 1310-1311are positioned at 90 cm, conductive ink can be designed and applied tofacilitate connecting to electrical connector 106 and cable 108. Theconductive sensors 1101-1108 and wires 1301-1308 need to be connected toan electrical connector 106 that is part of cable 108 that then connectsto the monitor 110. A specially designed conductive ink pattern willfacilitate connecting the conductive ink wires 1301-1308 to thiselectrical connector 106. In an exemplary embodiment, the electricalconnector 106 has conductive connection points lining the inner diameterthat when placed over the outer diameter of the tube 102 makeselectrical contact with the conductive ink pattern and completing anelectrical circuit.

C. Monitor Cable Design

In an exemplary embodiment, a cable 108 is used to connect a monitor 110with the feeding tube 102. In this exemplary embodiment, this cable 108is approximately 2 m long. At one end of the cable 108, a female RJ-45connector can connect with a male RJ-45 from the electrical connector106. At the other end of the cable 108, a male RJ-45 can connectdirectly into the monitor 110. The cable 108 can have protectivematerial that is appropriate for a clinical setting, such as resistingbodily fluids. The cable 108 is meant to be reusable.

D. Suction and Feeding Pump Connector Design

A tube connector 112 connects the feeding tube 102 to the tubes leadingto the feeding pump 116 and the wall suction 1110. In an exemplaryembodiment, the feeding tube 102 is used both to deliver the enteralfeed and to enable suction of stomach contents. In an exemplaryembodiment as shown in FIG. 14 a, the connector can have a “Y” pattern.The bottom portion 1402 of the connector 112 can connect to the feedingtube 102. The right side 1404 of the connector 112 connects to thefeeding pump tube 114 leading to the feeding pump 116. The left side1410 of the connector 112 connects to the suction tube 1109 leading tothe wall suction 1110. Enteral nutrition can follow the general pathfrom the feeding pump 116, down the feeding pump tube 114 into the tubeconnector 112, and then into the feeding tube 102. The specific path ofenteral nutrition within the connector 112 is the enteral nutritionenters the connector 112 at point 1412 and as the nutrition passescorner 1406 some tube feeds may go toward the left side 1410 of theconnector, but the nutrition will be blocked by valve 1408 that isclosed. Having been blocked by valve 1408, the enteral nutrition willpass point 1416 and proceed to back to bottom portion 1402. The valve1408 can take many exemplary forms with the key operating criteria thatwhen suction is applied the valve pulls open, but when fluid tries topush into the valve, it remains closed given the large pressuredifferences between suction and the feeding pump. Many exemplary valvesmay meet these criteria such as the umbrella type valve shown in FIGS.14A-14B, which may include, but is not limited to, butterfly valves,belleville valves, and duckbill valves. In some examples, a deformablesuction may be created on the vacuum pump side which collapses becauseof the pressure difference between the suction and atmospheric pressure.This deformable region may permit the check valve to open in thedeformed state and/or lower its stiffness.

In an exemplary embodiment as shown in FIG. 14A, suction can be appliedto remove the gastric contents. The wall suction 1110 is controlled atthe monitor 110 to a setting of being on or off. After the suction isturned on, the valve 1408 opens and enables the suctioning and removalof all gastric contents. These gastric contents are sucked up into thelumen of feeding tube 102 in a retrograde motion and into connector 112.Once in connector 112, they first pass point 1418, and then are drawn tothe left side 1410 and pass point 1420. The gastric contents thencontinue around valve 1408, past point 1422, and onward to a collectiontrap at the wall suction 1110 or monitor 110 location. In thisillustration, valve 1408 is in an open position due to the suctionforce. When suction is turned on, any tube feeds that may be coming fromthe feeding pump may also be suctioned into the suction tube 1109.Specifically, the tube feeds will enter on the right side 1404 and passpoint 1412. The suction force then draws all or a portion of the tubefeed around corner 1406 and past point 1414, where it continues aroundvalve 1408 and past point 1424. This suctioning of any tube feeds is notdetrimental to the patient since it is intermittent and clinicians candecide whether to discontinue or change the rate of administration oftube feeds. This connector 112 is designed to come with the feeding tube102 and thus be disposable along with the tube.

E. Monitor Design

The monitor 110 may comprise a computer (e.g., controller) and adisplay. The computer may be programmed (e.g., have access to a softwareprogram) to monitor patient conditions by receiving sensor data asdescribed herein, and to initiate and control actions of apparatuses asdescribed herein (e.g., provide commands or other signals to servos,pumps, voltage supplies, etc.). The monitor 110 may include a userinterface to allow input of data and commands to the monitor 110, suchas a touch screen display, a mouse, a track pad, a keyboard, amicrophone and voice recognition software, buttons, etc.

A “computer” refers to one or more apparatus and/or one or more systemsthat are capable of accepting a structured input, processing thestructured input according to prescribed rules, and producing results ofthe processing as output. Examples of a computer may include: astationary and/or portable computer; a computer having a singleprocessor, multiple processors, or multi-core processors, which mayoperate in parallel and/or not in parallel; a general purpose computer;a supercomputer; a mainframe; a workstation; a micro-computer; acontroller; a server; a client; an interactive television; a webappliance; a telecommunications device with internet access; a hybridcombination of a computer and an interactive television; a portablecomputer; a tablet personal computer (PC); a personal digital assistant(PDA); a portable telephone; application-specific hardware to emulate acomputer and/or software, such as, for example, a digital signalprocessor (DSP), a field-programmable gate array (FPGA), an applicationspecific integrated circuit (ASIC), an application specificinstruction-set processor (ASIP), a chip, chips, or a chip set; a systemon a chip (SoC), or a multiprocessor system-on-chip (MPSoC); etc.

“Software” refers to prescribed rules to operate a computer that may bestored in a computer-readable medium. Examples of software may include:code segments; instructions; applets; pre-compiled code; compiled code;interpreted code; computer programs; and programmed logic.

A “computer-readable medium” refers to any storage device used forstoring data accessible by a computer. Examples of a computer-readablemedium may include: a magnetic hard disk; a floppy disk; an opticaldisk, such as a CD-ROM and a DVD; a magnetic tape; a flash removablememory; a memory chip; and/or other types of media that can storemachine-readable instructions thereon.

A “computer system” refers to a system having one or more computers,where each computer may include a computer-readable medium embodyingsoftware to operate the computer. Examples of a computer system mayinclude: a distributed computer system for processing information viacomputer systems linked by a network; two or more computer systemsconnected together via a network for transmitting and/or receivinginformation between the computer systems; and one or more apparatusesand/or one or more systems that may accept data, may process data inaccordance with one or more stored software programs, may generateresults, and typically may include input, output, storage, arithmetic,logic, and control units.

A “network” refers to a number of computers and associated devices thatmay be connected by communication facilities. A network may involvepermanent connections such as cables or temporary connections such asthose made through telephone or other communication links. A network mayfurther include hard-wired connections (e.g., coaxial cable, twistedpair, optical fiber, waveguides, etc.) and/or wireless connections(e.g., radio frequency waveforms, free-space optical waveforms, acousticwaveforms, etc.). Examples of a network may include: an internet, suchas the Internet; an intranet; a local area network (LAN); a wide areanetwork (WAN); and a combination of networks, such as an internet and anintranet. Exemplary networks may operate with any of a number ofprotocols, such as Internet protocol (IP), asynchronous transfer mode(ATM), and/or synchronous optical network (SONET), user datagramprotocol (UDP), IEEE 802.x, etc.

Monitor 110 may serve several functions. For example, the monitor 110may function may analyze the reflux data, present a summary to theclinician in a simple and intuitive manner, analyze the reflux data inreal-time, initiate auto-suction if warranted, etc. . . .

The specific design of the monitor and display may differ from theexisting GERD related products that may also use impedance sensors. Thephysical design needs may include a display and a pole mountingconnector to be conducive to an ICU or acute care setting. The datadisplay may include both a summary of the reflux and suction events andthe ability to see the raw data captured by the sensors. For the summaryof reflux events, the data may be presented in text and/or graphicalform as presented in the exemplary embodiment shown in FIG. 15 . In thisexemplary embodiment, viewing the specific time period for when theimpedance data was collected can be set by input 1502 to a period of thelast 3 hours, 6 hours, 12 hours, or 24 hours. In this exemplaryembodiment, the text can be presented as a summary of the number ofreflux and suction events over the past 24 hours and the range of heightof the reflux events. For example, the display 1504 shows the number oftimes suction was triggered. The total number of reflux events in thelast 24 hours is shown in display 1506, as well as a summary of how manyreflux events achieved a specific height. The total number of swallowevents during the 24-hour period is shown in display 1508, and thenumber of belching events is shown in display 1510. An option forproviding more information on the patient history is to also have anarrow next to the number of events to denote whether the incidence ofreflux is increasing (up arrow) or decreasing (down arrow).

In graphical form, time may be represented on the x-axis, as shown indisplay 1512, and reflux height may be represented on the y-axis, asshown in display 1514. A summary of the impedance data that isdetermined to be a reflux event is represented as arrows, such as indisplay 1516, that are positioned at the time of the reflux event on thex-axis and with the height of the reflux represented as the length ofthe arrow along the y-axis. Suction events can also be noted on they-axis, such as in display 1518. A suction event or high level of refluxmay also be indicated by a visual alarm condition, such as the redcircle in display 1520. The area for display 1520 can also be used forconveying a non-alarm status, such as a green colored circle signifyingthat all measurements represent a normal or safe condition. Similarly, alow level of reflux or other combination of measurements can berepresented by a yellow colored circle signifying caution. Swallowevents can be shown, such as display 1522 and belching events can beshown, such as display 1524. The monitor may enable scrolling betweentime periods and zooming into specific time periods (expansion ofselected time periods) to see more detail. The monitor can also enableinput of other relevant data, such as when bolus feeding occurred, whenthere was a relevant event, such as spit-up/vomit, or when certaingastrointestinal-related medicines were taken. These additional data mayhelp put the impedance data in better context and thus help theclinician understand how the patient is doing. In addition to theimpedance data, the display can show a summary view of current andhistorical pH data, both for esophageal and stomach pH sensors.

In an exemplary embodiment, the monitor 110 can provide access to aninterface that enables setting preferences for the monitor 110 andfeeding tube 102, as shown in FIG. 16 . For example, setting preferencescan include actions such as determining whether to monitor swallows ornot, such as via input 1602. Settings can also include determiningwhether an alarm, as well as which type of alarm, should be initiated,such as via input 1604. Other alarm settings include the threshold uponwhich alarm is initiated, such as via input 1606, as well as the volumeof the alarm, such as via input 1610. Settings may also includeconfiguring the auto suction threshold, such as via input 1608. Forexample, the threshold can be configured to automatic, which is acombination of factors, or specifically to factors such as measuredreflux greater than 10 cm, greater than 15 cm, or greater than 5 cm forover 20 minutes.

In an exemplary embodiment, the detailed impedance and pH data arerecorded to a storage medium for later analysis. This storage medium canbe a flash card, or something else that is simple to access and transferto a PC for further analysis. Via an offline PC, the clinician can viewthe detailed impedance data collected since the measurements began.While viewing the data offline on a PC, a clinician may be able to inputinto the monitor 110 to add a reflux event and have it saved along withthe other noted reflux events.

In an exemplary embodiment, the form factor of the monitor may be asmall LCD or similar display adequate for readout. The monitor can havea size at least 3.5 inches diagonal and a minimum resolution of 320×480pixels in color. The monitor can have a flat bottom, and thus theability to rest on a shelf. A clamp accessory can enable connecting to arolling IV type poll.

The monitor 110 can run on wall current and have battery backupcontaining replaceable batteries. In another exemplary embodiment, themonitor 110 can have a battery backup containing an internalrechargeable battery.

In an exemplary embodiment, hardware buttons are designed to facilitateboth capturing and reviewing information. These buttons can facilitatecapturing events, such as the feeding, reflux, vomiting, feedingintolerance, and medication administration events. These buttons canalso have standard inputs for navigating and selecting items within themonitor UI. The buttons and monitor user interface can allow input ofthe patient's name and Medical Record Number.

In an exemplary embodiment, the screen is touch enabled, which can allowinteracting with the software user interface via touch gestures directlyon the screen. The monitor can also have a combination of a touchscreenand hardware buttons for interaction.

In an exemplary embodiment, the electronics of the monitor can beintegrated into an alternative device, such as the electrical connector106, tube connector 112, or a cloud-based computing device. In anexemplary embodiment, the electrical connector 106 can have all theelectronics integrated into its packaging. This can include allprocessing, memory and data connectivity. In this scenario, theprocessing of the impedance data can occur at the electrical connector106. The output of this processing can then be managed in multiple ways.For example, if during the processing of impedance data the algorithmsdetermined auto-suction should be initiated, a solenoid valve can beintegrated directly into the electrical connector 106 to initiatesuction. In this embodiment, the electrical connector 106 is no longer adisposable part of the tube, but instead can be reusable. Another waythe data can be managed is to enable viewing the summary data on analternate device. This alternate device can be a PC, a mobile phone, atablet, feeding pump, modular patient monitor or any other devicecapable of viewing the summary data. All set up and management functionsfor the feeding tube 102 that were previously described as occurring onthe monitor 110 can instead be accomplished via an alternative device.

In this embodiment, power can be supplied to the electrical connector106 to power the electronics. One option is to have a power cord thatconnects the electrical connector 106 to a wall outlet. This power cordcan be advantageously attached to the suction tube 1109. Alternatively,in combination with low voltage processing and memory technology it canbe possible to harvest the power from a number of potentiallyadvantageous mechanisms, such as piezoelectric, thermoelectric, solar,and battery technologies. In one exemplary embodiment, this battery canbe a standard battery situated within the electrical connector 106.

IV. Impedance Based Algorithms

A. Data Collection for Algorithms

In an exemplary apparatus, eight impedance sensors are utilized,consisting of two thin films where each thin film has four impedancesensors, as shown in FIG. 13 . These impedance sensors are locatedapproximately 2 cm apart. Two impedance sensors form one channel fordata collection. Therefore, among the four impedance sensors there arethree channels. Impedance is constantly measured between the two sensorsin each channel. An exemplary process for collecting data from theseimpedance sensors is shown in FIG. 17 .

The first step 1702 in the process is to capture data from all of theimpedance channels. The data collected from the impedance sensors is themeasurement of ohms between two sensors. The sensors do not necessarilyhave to be adjacent along the feeding tube. In the exemplary apparatus,the eight impedance sensors will therefore collect data as six channels.This data will naturally have small variations in a normal state withinthe esophagus, given factors such as minor changes in the esophagealenvironment. These small changes can be considered noise from aninterpretation perspective, so the raw data needs to be smoothed in step1704 in order to be processed in algorithms. Smoothing, which is a formof filtering, is the process of removing these minor variations in thedata so the data can be more easily processed in algorithms to determinethe patterns associated with specific conditions such as liquid reflux,gas reflux (belching), a swallow, or any combination. There are manyexemplary techniques for data smoothing that can be utilized in thisembodiment, including but not limited to moving average, least squares,exponential smoothing, and LOESS/LOWESS regression. The output of thissmoothing step is to create an impedance measurement that can be used inthe algorithms.

In an exemplary embodiment, the impedance data smoothing is calculatedusing an exponential moving average, as depicted by the formula below:

B _(t) =α×I _(t)+(1−α)×B _(t−1)

The coefficient α (alpha) represents the degree of weighting decrease.The coefficient alpha is a constant smoothing factor, where a higheralpha value discounts older impedance measurements faster. The variableI_(t) is the impedance measurement at any time period t. The variableB_(t) is the resulting impedance measurement after data smoothing at anytime period t.

The impedance measurement can then be analyzed in step 1706 to provideinformation about the status of the patient. In an exemplary embodiment,the derivative of the above impedance function can be calculated toprovide an indication of the rate of change in the impedancemeasurements. One exemplary way of calculating the derivative of thefunction Bt is via the following formula using Leibniz's notation:

d(B _(t))/dt=(B _(n) −B _(n−1))*F _(s)

The derivative of impedance may provide additional information forhelping to understand how quickly the impedance measurements aredropping, and therefore that a liquid reflux event may be occurring. Itcan also provide an indication if the impedance has reached a minimum ora maximum.

In another exemplary embodiment, the second derivative of the aboveB_(t) function can be calculated to provide an indication of when theimpedance has reached a minimum as opposed to a maximum. A shorterperiod to reach the lowest impedance measurement can better indicate areflux event, or potentially signify a stronger or faster reflux eventthat may put the patient at risk of aspiration.

One exemplary way of calculating the second derivative of the functionB_(t) is via the following formula using Leibniz's notation:

d ²(B _(t))/dt ²=(B _(n)−2*B _(n−1) +B _(n−2))*F _(s) ²

In an exemplary embodiment, the percent change in the impedancemeasurement is calculated to determine if there is a trend of impedanceincreasing or decreasing. One exemplary way of calculating the percentchange of impedance is the following:

$\frac{B_{m} - B_{n}}{B_{n}}$

In this exemplary embodiment, factor n, denoting the beginning timeperiod for calculating the summation, and the factor m, denoting theending time period for calculating the summation, can be determined by anumber of advantageous means. In one exemplary embodiment, the timeperiod for n or m can be calculated based on when the sign changes inthe percentage change calculation. In another exemplary embodiment, thefactor m can be calculated based on the second derivative of theimpedance measurement since the second derivative signifies when theimpedance measurement has reached a local minimum. In another exemplaryembodiment, the factor n, can be a fixed difference with factor m, wherevalues of the impedance measurement at time n and m are compared. If apredefined threshold based on the difference of the impedancemeasurement at time n and m is exceeded, n is set as the starting periodfor the summation. For example, the difference between time n and m canbe set as a fixed number such as (m−5) seconds. If the ratio of theresulting impedance measurement of time m over time n is 0.75, then timen and is set as the starting point for the summation.

After the change in impedance is calculated for each channel, thischange data is then compared between all eight channels in step 1708.For example, the time interval for any changes in baseline impedance inone channel is compared to the time interval of baseline impedancechanges in the other channels.

The change in the baseline impedance measurement for each channel isprocessed continually by algorithms to determine if the impedance changesatisfies the definition for a condition such as liquid reflux, gasreflux (belching), a swallow, or any combination. If the algorithmdetermines the definition of a condition has been met, this informationis then acted on a number of ways in step 1710, such as displayed on amonitor, signified as an alert, or processed in an algorithm todetermine any further action.

B. Algorithms for Detecting Liquid Reflux

The use of impedance sensors to measure reflux has been well establishedby products used to diagnose Gastroesophageal Reflux Disease (GERD). Themeasurement principle for impedance sensors is when reflux passes overadjacent sensors the impedance measured between these two sensorsdecreases. Impedance data collected from two sensors is defined as achannel. Liquid reflux has been generally defined as a retrograde 50%drop in the measured impedance in at least two adjacent channels, asdescribed by Zerbib, Frank et al, “Normal Values of Pharyngeal andEsophageal Twenty-four-Hour pH Impedance in Individuals on and offTherapy and Interobserver Reproducibility.” Clin Gastroenterol Hepatol.2013 April; 11(4):366-72, hereafter “Zerbib,” which is herebyincorporated in its entirety herein by reference. This definition ofreflux is based on relatively healthy patients being diagnosed for GERD.Zerbib also describes how only impedance drops lasting more than 3seconds are counted.

An example liquid reflux episode is shown in FIG. 18 . In this figure,the x-axis represents time and the y-axis represents the impedancemeasurements for each channel 1801-1806. In this exemplary embodiment,the six channels represent the eight impedance sensors 1101-1108.Specifically, channel 1 1801 represents the impedance measurement ofimpedance sensors 1101 and 1102. Similarly, channel 2 1802 representsthe impedance measurement for sensors 1102 and 1103, channel 3 1803represents sensors 1103 and 1104, channel 4 1804 represents sensors 1105and 1106, channel 5 1805 represents sensors 1106 and 1107, and channel 61806 represents sensors 1107 and 1108. As the impedance is measured inchannel 1 1801 at time one 1810 the impedance measurement starts todrop. The channel 1 1801 impedance measurement reaches a local minimumat time two 1812. If the difference in impedance between time one 1810and time two 1812 is greater than 50% that can signify that reflux hasbeen detected in channel 1 1801. A similar pattern of a drop inimpedance measurement is seen in channels 2 1802, 3 1803 and 4 1804.Since the time of the impedance drop is delayed in each successivechannel, it can signify that reflux is moving retrograde up theesophagus over time and is currently present in the location of channels1 through 4, 1801-1804. In channel 1 1801 at time three 1814 theimpedance measurement starts to increase. This increase continues totime four 1816, where the impedance measurement then levels off. Thisincrease and leveling off of the impedance measurement can signify thereflux is no longer present in the location of Channel 1 1801. Thisincrease in impedance measurement first started in channel 4 1804, andthen successively in channels 3, 2 and 1 1803-1801. This signifies thereflux reached a maximum height in the location of Channel 4 1804 andthen began to drop down in an antegrade motion through the locations ofchannels 3, 2 and 1 1803-1801. FIG. 18 illustrates a typical refluxevent, where reflux is seen moving retrograde up the esophagus and thencoming back down antegrade into the stomach.

While the same impedance measurement principles can be applied tomeasuring reflux in acute care patients, the algorithm may need to beadjusted to account for the unique parameters and condition of acutecare patients.

For example, in an acute care setting the emphasis is on protecting thepatient from the immediate threat of reflux potentially leading toaspirating gastric contents. This immediate threat is in contrast to theexisting use of impedance measurement and algorithms to diagnose GERD,which is a non-real time analysis performed hours or days aftercollecting all the impedance data from the patient. Therefore, themeasurements that trigger an alarm or suction event in an acute caresetting may be a lower threshold to ensure the patient is safe. Forexample, in an exemplary embodiment, liquid reflux may be defined as aretrograde 30% drop in the measured impedance from a combination of twodistal sensors compared to at least the next one or two proximalsensors. This definition may improve how potential reflux events arecaptured and processed in the algorithm.

This definition can also account for the fact that many acute carepatients are taking acid suppression medication, such as proton pumpinhibitors and H2 blockers. This acid suppression medication wouldresult in a higher pH value overall in acute care patients. This higherpH liquid is typically not as conductive as the lower pH liquid,potentially resulting in a smaller impedance change. The level ofimpedance may also change over time given the changing material in thegastric environment. Different medicines, foods, and the changingcondition of the acute care patient may also affect the impedancemeasurements.

A key difference in how existing impedance measurement systems work inidentifying GERD is the data is analyzed off line usually hours or daysafter the reflux events have already occurred, and thus not processed inreal time. Therefore, the current algorithms designed for GERD diagnosisare defined to identify the entire reflux episode, from the initiationof reflux until termination. The emphasis in a GERD diagnosis is to makesure the data is accurate in diagnosing a GERD condition, which willthen drive decisions about medication usage, such as acid suppressants,and diet. In contrast, in the acute care setting the data needs to beprocessed in real time and decisions on whether to initiate an alarm orsuction need to be made quickly in order to reduce the risk ofaspiration. In the acute care setting, therefore, the emphasis is ondetermining if reflux has potentially been initiated in each channel,and not waiting to determine if it has terminated. These are keydistinctions between modern impedance measuring systems and the proposedembodiment.

Given the importance of determining if reflux has been initiated, in anexemplary embodiment, it may be beneficial to use probability analysisto determine the relative probability that reflux has been initiated.For example, impedance measurements that indicate a larger impedancedrop over time may be assigned a higher probability. This may beimplemented on a graduated scale, such that the larger the impedancemeasurement drop, the higher the assigned probability. In contrast, asmaller impedance drop can be assigned a lower probability. Thisprobability analysis can also account for the measurements of multiplesensors. For example, as shown in FIG. 18 , if there is a progression oflower impedance measurements starting from the distal channels andcontinuing to the more proximal channels, the measurements from eachchannel can be assigned a higher probability since data from multiplechannels reinforces the definition that a reflux event is occurring. Incontrast, if only a proximal impedance channel were to suddenly showlower impedance measurements with no other neighboring impedancechannels showing reflux, the measurement can be assigned a lowerprobability.

C. Algorithms for Detecting Gas Reflux or Belching

The same apparatus and methods of use can also be used to detect refluxof a gas, often referred to as belching or burping. The proposedembodiment can discriminate air, or any belched gas, since it is a verypoor conductor and thus typically causes an increase in impedance (e.g.from 4000 to 5500) versus the decrease in impedance caused by liquid(e.g. from 4000 to 2000) which is much more conductive. Traditionally,gas reflux is defined as a rapid (3 Kohm/s) increase in impedance >5Kohm, occurring simultaneously in at least two impedance channels, asdescribed in Zerbib. An example of gas reflux is showing in FIG. 19 .

In this figure, the x-axis represents time and the y-axis represents theimpedance measurements for each channel 1801-1806. In this exemplaryembodiment, the six channels represent the eight impedance sensors1101-1108. As the impedance is measured in channel 1 1801 at time one1910 the impedance measurement increases very quickly. At time two 1912the impedance measurement subsequently drops very quickly. The impedancemeasurement for channels 2 through 6 1802-1806 also increase anddecrease at time one 1910 and time two 1912 respectively. This patterncan signify a belch event, since the impedance rises very quickly andsimultaneously across each channel, representing gas from a belch movingretrograde quickly up the esophagus.

Detecting gas reflux in patients may be beneficial by allowing detectionof those with gas forming bacteria in their stomach or small bowel. Thiscan be an indicator of overgrowth with non-resident bacteria, which alsocauses other symptoms (e.g. bloating) and signs (e.g. diarrhea).Belching is a sign of feeding intolerance. Therefore, a patient thatexhibits excessive belching may require different treatment by theclinician. Treatment can generally follow treatment for feedingintolerance, such as reducing tube feeds, raising the head of bed,administration of prokinetic agents, etc.

D. Algorithms for Detecting Swallows

The same apparatus for measuring reflux can also detect, record andreport swallowing events. A swallow is an antegrade movement of aconductive material, e.g. saliva, food, drink, down the esophagus.Impedance measurement data of a typical swallow is shown in FIG. 20 .

In this figure, the x-axis represents time and the y-axis represents theimpedance measurements for each channel 1801-1806. In this exemplaryembodiment, the six channels represent the eight impedance sensors1101-1108. The impedance measurement in channel 6 1806 begins to drop attime one 2010. Since the first change in impedance measurement comesfrom the proximal channel 6, it signifies bolus material such as food orliquid is moving antegrade from the oropharynx and down the esophagus.The channel 6 1806 impedance measurement reaches a local minimum at timetwo 2012. If the difference in impedance between time one 2010 and timetwo 2012 is greater than 50% that can signify that bolus material hasbeen detected in channel 6 1806. A similar pattern of a drop inimpedance measurement is seen in channels five 1805, 4 1804, 3 1803, 21802 and 1 1801. Since the time of the impedance drop is delayed in eachsuccessive channel, it can signify that bolus material is movingantegrade down the esophagus over time and is successively present inall six channels 1801-1806. In channel 6 1806 at time three 2014 theimpedance measurement starts to increase. This increase continues totime four 2016, where the impedance measurement then levels off. Thisincrease and leveling off of the impedance measurement can signify thebolus material is no longer present in the location of Channel 6 1806.This increase in impedance measurement first started in channel 6 1806,and then successively in channels 5, 4, 3, 2 and 1 1805-1801. Thissignifies the bolus material progressed from Channel 6 1806 and droppeddown in an antegrade and motion through the locations of channels 5, 4,3, 2 and 1 1805-1801. FIG. 20 illustrates a typical bolus materialswallow event, where bolus material is seen moving antegrade down theesophagus and into the stomach.

Understanding the frequency and pattern of swallowing can be helpful toclinicians. For example, it may be a sign that they are becoming moreconscious. This can be important for patients who are sedated in an ICUwhere their level of sedation and consciousness needs to be monitoredclosely in order to titrate the administration of sedative drugs. If apatient requires paralysis, e.g. for life threatening hypoxemia, thefrequency of swallows can also be used to titrate the administration ofparalytic drugs, e.g. cisatricurium, rocuronium, with initiation ofswallowing revealing a wearing off of the desired paralysis. In anotherexample, a patient after a traumatic brain injury or after a severestroke may be in a coma and also have impaired swallowing. Seeing aresumption of swallowing or increase in the frequency can be animportant clue to clinicians that the patient is recovering neurologicfunction. In contrast, failure to resume such swallowing can be apotential sign that the brain injury is not improving.

E. Algorithms for Detecting Mixed Conditions

The algorithms need to account for scenarios where there are mixedconditions. For example, a patient that is swallowing may also besimultaneously refluxing gastric contents. An example of impedancemeasurements showing both swallowing and reflux is shown in FIG. 21 .

In this figure, the x-axis represents time and the y-axis represents theimpedance measurements for each channel 1801-1806. In this exemplaryembodiment, the six channels represent the eight impedance sensors1101-1108. The impedance measurement in channel 6 1806 begins to drop attime one 2110 and begins to level off at time three 2114. Since thefirst change in impedance measurement comes from the proximal channel 6,it signifies a swallow, i.e. bolus material is moving antegrade from theoropharynx and down the esophagus. At time two 2112, the impedancemeasured in channel 1 1801 starts to drop and then levels off at timefour 2116. The change in channel 1 1801 signifies that reflux ispresent. Channels 5 1805 and 4 1804 also indicate a swallow event.Channels 2 1802 and 3 1803 indicate reflux is present. FIG. 21illustrates a combination event where the swallow and reflux event occurat roughly the same time.

A swallow measurement can potentially mask a reflux event. Therefore, itis important to ensure that reflux is accurately assessed in these mixedconditions since the patient may be at risk for aspiration.

Another example of a mixed condition is a combination of liquid and gasreflux, or mixed reflux. This mixed reflux may be measured as gas refluxoccurring immediately before or during a liquid reflux measurement. Inan exemplary embodiment, additional algorithms can be created tocorrelate gas reflux with liquid reflux. For example, if there is apattern where gas reflux occurs before liquid reflux, interventions canpotentially be initiated before any liquid reflux is measured. Anotherexemplary embodiment is correlating swallows with liquid reflux. A lackof swallows measurements can indicate the patient is at a higher riskfor aspiration. Therefore, interventions may be initiated earlier ormore quickly, and based on alternative interpretations of potentialreflux.

F. Algorithms for Smart Alarms

Alarms may be beneficial for warning of potential aspiration based onreflux and other measurements. The device can have an option for turningon one or more alarms. An alarm can be triggered, for example, for anyreflux event. This, however, may lead to “alarm fatigue” in a patientwith multiple small episodes of reflux. Therefore, it is desirable toallow customization of alarms based on the clinician's preferences withrespect to a particular patient. For example, it may be desirable to setthe threshold for triggering the alarm to be if any of the followingconditions are met: 1) any reflux event of at least 10 cm inexcursion/height, 2) the presence of at least 5 episodes of reflux lessthan 10 cm in height over a 6 hour period, 3) the continuous presence(at least 15 minutes) of a conductive material (likely liquid) spanningthe sensors closest to the head, 4) a rapid rate of detecting animpedance drop in multiple channels.

There can be an option for a visual alarm only, an audio alarm only, ora combination of a visual and audio alarm. The visual alarm can consistof a blinking red light that is part of the user interface, as shown inFIG. 15 . There can be an option to allow customization of the soundlevel of the audio alarm. In addition, there can be an option to fordifferent levels of alarm based on the nature of the reflux. Forexample, it may be desirable to have a visual alarm only for refluxevents that may be of less concern, for example, less than 5 cm inheight. However, if a reflux event between 10-15 cm in height isobserved this can trigger the addition of the audible alarm. The systemcan also allow for escalation of the alarm volume, for example, if the“alarm silence” button is not enabled to show acknowledgement of thealarm state, the alarm volume can escalate over 5 minutes to the highestvolume possible. The alarm state can also be transmitted, for example,wirelessly to a nurse's station, mobile phone, PC, feeding pump, modularpatient monitor, or other device. In addition to use of reflux frequencyand height, the alarm triggering threshold can also take into accountdata such as pH data, level of feeding, level of motility, plus specificdata on the patient, i.e. medical condition, age, weight, etc.

V. Aspiration Prevention Interventions

There are several approaches to preventing aspiration in enterally fedpatients, including “passive” and “active” systems.

A passive system may simply provide information to the clinician andsolely relies on the clinician's response to this information to changethe management of the patient. In one example, the feeding tubecontinuously records the presence of a conductive material (e.g. gastriccontents) in the esophagus, and a pattern of retrograde bolus movementconsistent with reflux of gastric contents is observed. These data arepresented on the monitor. If the clinician is concerned about these datathey can change the management of the patient. Some common responsesinclude, but are not limited to, one or more of the following: 1)temporarily stop or reduce the rate/volume of tube feeds; 2) initiateadministration of a prokinetic agent, e.g. erythromycin ormetoclopramide, to enhance gastric emptying; 3) increase the elevationof the head of bed, e.g. from 30 to 45 degrees, in order to use gravityto minimize superior excursion of refluxed gastric contents; 4) switchfeeding tube from gastric tube (naso- or oro-gastric) to a post-pylorictube, ideally distal to the Ligament of Treitz; 5) manually suction outgastric contents.

After one or more of these interventions, the clinicians can determineif they have achieved a reduction in the frequency and/or superiorexcursion of refluxed gastric tube feeds. They can also determine ifthere is reduced bolus presence in the esophagus.

While there are many benefits to a passive system, in many clinicalcontexts there can be substantial incremental benefit from an activesystem. In addition to sharing the data collection features of thepassive system, an active system has at least one automatedintervention. This automated intervention has the benefit of beingexecuted immediately once specific criteria have been met. In anexemplary embodiment, impedance data is captured and then analyzed viaalgorithms to determine if the specific criteria have been met. In oneexemplary embodiment, the criterion is reflux detected at the highestimpedance channel, signifying a higher probability of a potentialaspiration event. In another exemplary embodiment, the criterion is theoccurrence of reflux events at lower channels over a specific period,also potentially signifying a higher probability of a potentialaspiration event. A number of exemplary data and criteria can be used toinitiate an active process of intervention.

In one exemplary active system, once the criteria have been met thecomputer 110 may initiate processes (e.g., control appropriate pumps) sothat gastric contents are automatically suctioned out of the stomach,which may assist in preventing gastric contents from being aspirated. Inanother exemplary active system, once the criteria have been met thefeeding pump is automatically turned off by the computer so noadditional feeds are introduced into the stomach, which may reduce anygastric contents from potentially being aspirated. In another exemplaryactive system, the computer may cause an obstruction to be automaticallycreated in the esophagus, which may assist in preventing gastriccontents from being aspirated.

A. Aspiration Prevention Via Suction of Gastric Contents

Applying suction to the feeding tube removes gastric contents and thuscan potentially prevent or minimize subsequent aspiration since lessmaterial is present in the stomach and esophagus that can potentially beaspirated into the lungs. The general concept is an apparatus and systemas shown in FIG. 11 that monitors reflux. When a certain frequency orsuperior excursion of reflux is measured or when there is a certainlevel of bolus presence in the esophagus, suction is transiently (e.g. 3minutes) applied to the feeding tube to remove most or all of thegastric contents. In an exemplary embodiment, it may be desirable to setthe threshold for triggering automatic suction to be if any of thefollowing conditions are met: 1) any reflux event of at least 10 cm inexcursion/height, 2) the presence of at least 5 episodes of reflux lessthan 10 cm in height over a 6 hour period, 3) the continuous presence(at least 15 minutes) of a conductive material (likely liquid) spanningthe sensors closest to the head, 4) a rapid rate of detecting animpedance drop in multiple channels.

In an exemplary embodiment, the auto-suction product is comprised of areflux detecting feeding tube, a connector for attaching the enteralfeeding tube and suction tube, a monitor with auto-suction capability orcontrol and containing a software component with customizable options tomanage the process, as shown in FIG. 16 .

In one exemplary embodiment, the feeding tube/impedance catheter has adedicated suction lumen. For the apparatus containing a dedicatedsuction lumen, one lumen can be accessed for delivery of enteral feedsas well as medications, and the other lumen is connected to themonitor's suction device.

In an exemplary embodiment, there is a shared lumen such that no spacewithin the tube is wasted on a lumen for suction that may never beneeded. In a feeding tube with the shared lumen, an exemplary connectoris attached to the proximal side of the feeding tube and has 2connections or ports as shown in FIG. 14 . One port connects to theenteral feeding tube where feeds are introduced, either bolus or via aninfusion pump. The other port connects to a tube that is connected to adevice which provides suction which can be provided by the monitor witha built-in suction capability, or it can be provided by standardhospital wall suction where the monitor exercises control of thesuction.

During suction, one can envision automation of the feeding infusion pumpto decrease or transiently stop infusion of tube feeds, however, this isnot necessary, as a transient vacuum is more than adequate to reduce thestomach contents. Infusion rates of food are generally no more than 1.5ml/min, therefore, even if feeding is not stopped there is minimaladditional gastric contents achieved over the short run. In addition,there may be a benefit to not stopping tube feeds in patients who are atincreased risk for hypoglycemia, e.g. patients on insulin who may becomehypoglycemic if feeding is completely stopped.

The monitor's auto-suction system has several embodiments. In oneembodiment, the monitor contains its own vacuum source, e.g. internal tothe monitor. This must be able to generate 50 to 150 mm Hg negativepressure. In this embodiment, plastic tubing is connected from the“patient side” connector on the monitor to the suction port of thefeeding tube connector. For ease of use this tubing can be connected tothe feeding tube's electronic connecting apparatus and tubing used forinfusing feeding, so only one apparatus contains up to 3 functionalgroups, i.e. wiring, feeding tubing, suction tubing. If the monitordetects specific triggering criteria, the vacuum system in turned on fora transient period, e.g. 3 minutes, in order to remove all or most ofthe gastric contents. An alarm can be triggered to notify the cliniciansthat such an intervention occurred. The system can automatically resetsuch that if it detects additional triggering criteria additionalsuction is applied. A lockout can be set such that if desired theapparatus must wait at least 15 minutes in between suctioning events, tominimize potential damage to the stomach's mucosa (lining).

In a preferred embodiment, the system relies on externally providedsuction, e.g. the hospital's wall suction, as shown in FIG. 11 . In thisembodiment, the monitor controls a 2 way normally closed solenoid valve.In this embodiment, plastic tubing is connected from the hospital'sroutine wall suction regulator (reduces maximum pressure toapproximately 150 mm Hg and allows for manual adjustment of suctionpressure), passes through the monitor, and then connects to the suctionport of the feeding tube connector, as shown in FIG. 14 . For ease ofuse this tubing can be connected to the tube's electronic connectingapparatus and the tubing used for infusing feeding, so only oneapparatus contains up to 3 functional groups, i.e. wiring, feedingtubing, suction tubing.

If the monitor detects specified triggering criteria, the solenoid valveis energized for a transient time (e.g. 3 minutes) resulting in it beingopened such that the external vacuum source is connected with the tubingconnected to the patients feeding tube, in order to remove all or mostof the gastric contents. An alarm can be triggered to notify theclinicians that such an intervention was made. The system canautomatically reset such that if it detects additional triggeringcriteria an additional suction is applied by reenergizing the solenoidvalve. A lockout can be set such that if desired the apparatus must waitat least 15 minutes in between suctioning events.

Regardless of whether suction is internally or externally acquired,there is a need for a disposable suction trap as routinely employedduring suction events. For example, the disposable suction trap can belocated between the feeding tube connector 112 and the monitor 110.

The valve mechanism can be located in multiple places. For example, thevalve for opening and closing suction can be located at the actualmonitor. Another embodiment is to locate the valve at the head of thefeeding tube. This can allow the feeding pump tube and the suction tubeto be attached as-is to the feeding tube. In one exemplary embodiment,the valve can be connected via the wires that run back to the monitorand thus controlled via the monitor. In another exemplary embodiment,the control of the valve can be integrated directly into the valveassembly. In this embodiment, there may not be a physically separatemonitor. The monitor functions are essentially integrated into theconnector component. This includes functions such as monitoring theimpedance measurements, controlling the valve for suction, initiatingany alarms and managing settings.

There are a number of criteria for triggering suction. In one exemplaryembodiment, a higher frequency of reflux events triggers suctionregardless of the height of this reflux event, e.g. 1 event 5 cm inheight may not trigger suction, however, 5 of these events over 30minutes may trigger suction. In another exemplary embodiment, superiorexcursion of reflux, e.g. reaching 10 or 15 cm, triggers suction, evenif there is only 1 such event. Alternatively, a single event of refluxrising to above the carina can trigger the suction. The rate ofdetecting reflux in each channel can also trigger suction. For example,suction can be initiated when reflux is detected in each successivechannel at a fast rate, such as one channel per second (2 cm/s) startingin the distal channels. This fast rate of detected reflux can signifyaspiration may occur imminently and thus the patient is at a higherrisk. The size of the reflux, or bolus, can also be a trigger forsuction. For example, a bolus spanning two channels, therefore 4 cm, cantrigger suction if measured in the more proximal channels that arecloser to the tracheal opening 107. This may also be customized based onpatient factors. For example, in another exemplary embodiment, in apatient who is 3 days postoperatively from a lung transplant it may bedesirable to suction tube feeds if any reflux is detected, e.g. only one5 cm high event. In another exemplary embodiment, the monitor maycompute a risk factor based many inputs such as the number of refluxeswithin a time period, the extent of those refluxes, the rate of theretrograde motion of the reflux, the number of swallows within a timeperiod, the number of belches in a time period, etc. For example, eachreflux may be assigned a numerical severity based on its extent, rate ofretrograde motion, and volume of the reflux. The risk factor may becomputed from these severities with a sliding weight function. Thisweight function may place the most weight on the severity of the mostrecent refluxes with a decreasing weight given to the severity ofrefluxes which happened earlier. The risk factor may be computed as thesum of the weighted severities of each of the refluxes. The suction maybe initiated if the risk factor was above a certain threshold. Theweighing and severity functions may be designed to produce a risk factorabove a default threshold for a rapid and extensive reflux happening inreal time. Other events such as swallows or even suction may be assigneda negative severity and consequently reduce the risk factor. Theclinician may be able to view this risk factor displayed on the monitor.The embodiments of the display risk factor include but are not limitedto text, a colored indicator, the risk factor plotted with respect totime, and a bar graph.

Suction is routinely applied to gastric tubes, typically either ascontinuous low suction (e.g. 30-50 mm Hg) or intermittent high suction(e.g. 150 mm Hg). There is generally a desire to minimize continuoussuctioning with high suction in order to avoid damage to the gastricmucosa (i.e. stomach lining). Therefore, a default setting may call for3 minutes of suctioning, however, this can be changed based on cliniciandesire. In addition, the suctioning duration can escalate based onrecorded data. For example, if reflux is still very active after 3minutes of suctioning, the monitor (in addition to alarming and alertingthe caregiver) can apply constant suction (up to a maximum of 30minutes) until the reflux abates. In addition, it may be possible forthe monitor to vary the suction strength. For example, for the monitorwith the internal vacuum source, it is possible to customize the systemsuch that upon less concerning reflux (e.g. 3 events×5 cm in height over1 hour) 3 minutes of low vacuum pressure (e.g. 50 mm Hg) is applied,however if there is very concerning reflux (e.g. 2 events×15 cm inheight) then full strength suction (e.g. 150 mm Hg) is applied.Similarly, in the case where the monitor is controlling suction, anexemplary valve can open up part way to initiate low vacuum pressure(e.g. 50 mm Hg), but be open fully to initiate full strength vacuumpressure (e.g. 150 mm Hg). In other exemplary embodiments there can bevariations of this transition from low vacuum pressure to full strengthvacuum pressure. For example for the first minute the monitor caninitiate full strength vacuum pressure but then lower it to low vacuumpressure for the remaining two minutes. In another exemplary embodiment,the monitor can initiate full strength vacuum pressure until the levelof reflux has declined to a sufficient point.

To help the clinician understand the suction events, there can also bethe option for a report that tells the clinician how many suctioninginterventions were triggered in a time period, e.g. 6 or 24 hours. Thisreport can contain detailed information about the measurements before,during, and after the suction event.

In such a setting where reflux of gastric contents is monitored andeither passive or active interventions can be triggered there may be noneed for routine, manual measurements of Gastric Residual Volume (GRV).This can reduce the workload of nurses since measurement of GRV is atime consuming task. It is done to try to identify patients at higherrisk for reflux and aspiration since currently there is no way ofdetecting if patients are exhibiting reflux.

In an exemplary embodiment, the algorithm may be adjusted to reflect howthe head of bed angle affects the measurement of reflux and thepotential risk of aspiration. A lower head of bed angle is common inacute care patients. The guidelines recommend a head of bed angle of atleast 30° for acute care patients. Often these patients slide down intheir beds for an effective angle of less than 30°. Many patients arenot monitored that closely, so the effective angle of the patient isquite often less than 30°. The specific sensor location of any measuredreflux and the length of time the patient is refluxing can affect whento initiate suction. In an exemplary embodiment, a lower proximallocation of reflux and a shorter length of time refluxing may beutilized to initiate auto suction given patients are often at a lowereffective head of bed angle and may more easily reflux and aspirategastric contents. For example, reflux measured at a sensor location of 5cm, which is approximately 5 cm above the LES, is may be specified toinitiate suction. In another example, reflux measured for a period offive minutes at a location of 5 cm above the LES may be specified toinitiate suction.

The ability to detect reflux and suction gastric contents can evenenable a lower head of bed than is now routinely prescribed due in theabsence of these useful tools. This lower head of bed may enable anumber of benefits. In some patients with head injuries, it isbeneficial to have a lower head of bed angle to assist in the recoveryof the patient. It may also be feasible that a lower head of bed anglecan help prevent subglottic secretions that contain oropharyngealbacteria from colonizing the trachea 107 and raising the risk ofaspiration pneumonia. In each case, the suction capability of theproduct can reduce the patient's risk of aspirating gastric contents andpotentially developing aspiration pneumonia.

Acute care patients with a feeding tube may be more susceptible toreflux since the feeding tube passes through the LES and therefore cansometimes compromise the effectiveness of the LES in preventing gastriccontents from entering the esophagus. Therefore, reflux may be detectedin the distal channels, such as 5 cm above the LES, more frequently. Inan exemplary embodiment, suction may only be initiated if reflux reachesthe higher proximal channels, since reflux may be more common at thelower distal channels.

B. Aspiration Prevention Via Adjustment of Feeding Pump

Data provided by the impedance sensors may be used to adjust feedinglevels. For example, if the patient is experiencing reflux past apredetermined level, the feeding pump may be instructed to decrease thelevel of feeding, e.g. from 80 ml/hr to 40 ml/hr. This decrease infeeding may allow the patient to further digest the nutrition, and mayprevent a more severe episode(s) of reflux from occurring that wouldincrease the risk for aspiration. In this example, the smart feedingtube is connected to a feeding pump, enabling a direct connection tocapture and process impedance data and then make changes to the deliveryof nutrition. An alarm may also be added to the device to communicate toclinicians of any reflux events and when the feeding level has beenreduced.

Many clinicians initiate nutrition at a very low rate given the fear ofreflux and aspiration of gastric contents. Such a system as describedabove can enable clinicians to initiate feeding at a higher rate andwith more confidence, knowing that if any clinically significant refluxis detected, the feeding rate can be automatically decreased and/or thegastric contents automatically removed via suction. This can enableacute care patients to receive more nutrition, and therefore recovermore quickly and effectively while also being protected from potentialaspiration of gastric contents.

C. Aspiration Prevention Via Esophageal Obstruction

Another exemplary embodiment prevents aspiration by automaticallyinitiating an obstruction in the esophagus in response to the impedancesensor data that can prevent gastric contents from traveling up theesophagus to the trachea's opening 107. A balloon device may be locatedsomewhere between the LES and trachea 107, automatically inflate basedon the sensor data. If the level of reflux measured by the sensors1101-1108 is high enough to indicate that the patient is at risk ofaspiration, the monitor may control a pump to pump air into the balloonand inflate the balloon. The inflated balloon creates a barrier in theesophagus 101 that prevents the reflux from getting to the trachea 107and potentially entering the lungs. This same approach may also be usedto prevent vomiting upon detection of a risk of vomiting by the monitor.The balloon mechanism should inflate quickly enough to block any reflux.The algorithm for determining when to inflate can correspond with thespeed of inflation. The materials of the balloon and level of inflationare designed to accomplish the goal yet not injure the esophagus 101.After inflating, the balloon can ideally be used again. The monitor canshow information about the balloon being deployed. An alarm may also betriggered to warn clinicians when such a severe reflux or vomit eventoccurs so they can potentially attend to the patient. As the balloon isinflated, the gastric contents may automatically be removed via suctionas discussed elsewhere herein.

It should be emphasized that the embodiments disclosed herein are notmutually exclusive but are useable with one another, in whole or inpart—it is impracticable to set forth a separate description to for eachpossible combination of features of the embodiments described herein,and thus a particular combination of features according to the inventionmay be described in connection with separate embodiments in thisdisclosure. Some embodiments utilize sensors to assist the clinicianplace the feeding tube correctly in the patient. Such embodiments mayreduce time and expense to confirm the placement (e.g., via an X-ray).These embodiments may allow clinicians to insert feeding tubes andprovide timely feedback to indicate that the insertion is correctlyplaced, or progressing correctly or that the feeding tube is not in acorrect location, such as the lumen of the trachea or a bronchus. Someembodiments provide feedback to indicate that enteral nutrition is beingtolerated, or, as appropriate, warning the clinician that enteralnutrition is not being tolerated. Gastric residual volume may beautomatically measured via a sensor, which may ease the burden onclinicians in connection with manual measurements or other laborintensive measurements. Some embodiments assess gastric motility, aclinical read-out that can help clinicians determine if patients aretolerating enteral nutrition. According to other embodiments, reflux inthe esophagus may be monitored, providing both a warning to cliniciansand an automatic suction capability to remove the gastric contents andthe risk of aspiration. While example embodiments have been particularlyshown and described, it will be understood by one of ordinary skill inthe art that variations in form and detail may be made therein withoutdeparting from the spirit and scope of the attached claims.

VI Impedance Based Local GRV Estimation

In an exemplary embodiment, a sensor located at the distal end of thefeeding tube is used to measure GRV. The GRV sensor may be composed oftwo or more electrodes. When these electrodes are placed in thepatient's stomach, they measure the impedance of nearby tissue andfluids. This impedance measure will depend on the conductivity anddistribution of the tissues and fluids surrounding the electrodes. Sincethe gastric chyme typically has a high conductivity relative to thestomach or other surrounding tissue, as the volume of the stomachincreases due to an increase in gastric chyme, the impedance measured bythese electrodes will decrease. This decrease in impedance may occur dueto the creation of a larger path width between the electrodes created bythe gastric chyme. If the GRV sensor is composed of just two electrodes,this will be referred to as a bipolar impedance sensor/measurement. Withtwo electrodes, impedance may be measured by injecting a current betweenthe two electrodes and simultaneously measuring the resulting voltage onthe same two electrodes. These two electrodes simultaneously work asboth the current source electrodes and the voltage sensing electrodes.If the GRV sensor is composed of three electrodes, this will be referredto as a tripolar impedance sensor/measurement. With three electrodes,impedance may be measured by injecting a current between a commonelectrode and a source electrode. The voltage is then measured between asensing electrode and the common electrode. The common electrodefunctions as both a source electrode and a sensing electrodesimultaneously. If the GRV sensor is composed of four electrodes, thiswill be referred to as a tetrapolar impedance sensor/measurement. Withfour electrodes, impedance may be measured by injecting a currentbetween two source electrodes and the voltage may be measured betweentwo sensing electrodes. In some embodiments, impedance may also bemeasured by applying a voltage to the source electrodes and measuringthe resulting current on the sensing electrodes in bipolar, tripolar,and tetrapolar impedance measurement configurations. Two or moreelectrodes may be ganged together to form a single electrode. Forexample, two or more electrodes on a conductivity sensor may function asa single electrode for the GRV sensor by electrically connecting theseelectrodes, such as outside the patient, such as within the monitor.

In an exemplary embodiment, a conductivity sensor may also be located atthe distal end of the feeding tube along with the GRV sensor. Theconductivity sensor can be utilized to determine the conductivity(inverse of resistivity) of the gastric contents. The conductivitysensor functions in the much the same way as an impedance sensor, but itis intended to only measure the intrinsic property of electricalconduction of a relatively well-known volume of tissue or liquid. Bycontrast, the impedance measurement of the GRV sensor is a reading ofthe extrinsic property of electrical conduction of a volume of liquidsand tissues whose conductivity and distribution is unknown. Similar tothe GRV sensor, the conductivity sensor may be composed of two, three,or four electrodes. If the conductivity sensor is composed of just twoelectrodes, this will be referred to as a bipolar conductivitysensor/measurement. With two electrodes, conductivity may be measured byinjecting a current between the two electrodes and simultaneouslymeasuring the resulting voltage on the same two electrodes. These twoelectrodes work as both the current source electrodes and the voltagesensing electrodes. If the conductivity sensor is composed of threeelectrodes, this will be referred to as a tripolar conductivitysensor/measurement. With three electrodes, conductivity may be measuredby injecting a current between a common electrode and a sourceelectrode. The voltage is then measured between a sensing electrode andthe common electrode. The common electrode functions as both a sourceelectrode and a sensing electrode simultaneously. If the conductivitysensor is composed of four electrodes, this will be referred to as atetrapolar conductivity sensor/measurement. With four electrodes,conductivity may be measured by injecting a current between two sourceelectrodes and the voltage may be measured between two sensingelectrodes. In some embodiments, conductivity may be also be measured byapplying a voltage to the source electrodes and measuring the resultingcurrent on the sensing electrodes in bipolar, tripolar, and tetrapolarconductivity measurement configurations.

FIG. 22A shows an exemplary embodiment of a tetrapolar conductivitysensor at the distal end of the feeding tube 102. It is composed ofsource electrodes, 2201 and 2202, and two sensing electrodes, 2203 and2204. Electrodes 2201 and 2202 may also be used in bipolar conductivitymeasurement configurations to simultaneously inject current and sensevoltage as shown in FIG. 22E. This conductivity measurement can behelpful for estimation of GRV, since the estimation of GRV usingmeasurements of epigastric impedance (see FIG. 10 ) depends onconductivity of the gastric contents and the other structures (e.g.,skin, muscle tissue, adipose tissue) and their volumes in the epigastricregion being interrogated by the GRV sensor's impedance measurementelectrodes. The stomach contains relatively conductive material and whenGRV increases, the measured impedance decreases. An increase in theconductivity of the gastric contents will also cause a drop in themeasured impedance. By measuring the conductivity, this confoundingimpedance variable can be factored out from the estimation of GRV. Byextension, the measurement of GRV via impedance depends on a differencein impedance of the gastric contents and these other structures. If theionic strength of the tube feeding formula is too low, then thedifference in impedance between the gastric contents and the otherstructures in the epigastric region of interest will be insufficient toprovide a reliable signal for estimating GRV. In the researchlaboratory, this problem can be solved in a simple way by adding a largequantity (e.g., 9 g/L; 154 mEq/L) of sodium chloride (NaCl; table salt)to the standard tube feeding formula to ensure that the ionic strengthof the tube feeding formula is sufficient to provide a good impedancesignal for estimation of GRV. In the clinical setting, however, it wouldbe ill-advised to add large quantities of sodium chloride to the tubefeeding formulas that are administered to patients, since many patientscannot tolerate large loads of either sodium ion (Na+) or chloride ion(Cl−). Some commercial tube feeding formulas contain high concentrationsof Na+ and potassium ions (K+), and therefore have sufficient ionicstrength to permit reliable estimates of GRV, using the epigastricimpedance methodology. One such formula is Osmolite 1.2, which contains58 mEq/L of Na+ and 46 mEq/L of K+. Other commercial tube feedingformulas contain relatively low concentrations of Na+ and K+, andtherefore may not have enough ionic strength to permit reliableestimates of GRV, using the epigastric impedance methodology. An exampleof this type of tube feeding formula is Nutrihep, which contains 7 mEq/Lof Na+ and 33 mEq/L of K+. The ionic strength (and, hence, theconductivity) of the gastric contents is determined not only by theionic composition of the tube feeding formula, but also by the secretionof ions (H+, K+, Cl−) by the gastric mucosa into the lumen of thestomach. Thus, in order to determine whether the contents of stomach atany given point in time have a composition that is suitable fordetermination of GRV, it may be desirable to continuously monitor theconductivity of the gastric contents. Moreover, since calibration of theepigastric impedance monitoring system (by injecting into the stomach aknown volume of tube feeding formula) will be done only intermittentlyand the rate and composition of gastric secretion of ions can change ona minute to minute basis, it may be useful to adjust the GRV calibrationsettings continuously by taking into consideration measured changes(relative to the value measured at the time of calibration) of theconductivity of the gastric contents.

In an exemplary embodiment, the calculation of impedance is based on thefollowing exemplary equation according to Jaakko Malmivuo & RobertPlonsey, “Bioelectromagnetism—Principles and Applications of Bioelectricand Biomagnetic Fields”, Oxford University Press, New York, 1995,25.3.3, hereafter “Malmivuo” which is incorporated in its entiretyherein by reference.

$Z = \frac{Z_{t}Z_{s}}{Z_{t} + Z_{s}}$

In the above exemplary equation, there is an assumption that the tissueoutside the stomach and the stomach are essentially parallel resistors.In an exemplary embodiment, there is an assumption that the impedance ofthe surrounding tissue (Z_(t)) is constant.

In this exemplary embodiment, the impedance of the stomach (Z_(s))varies as a function of its conductivity (σ), length (l) andcross-sectional area (A_(s)), which is perpendicular to the flow ofcurrent. In this exemplary embodiment, there can be an assumption thatthe length is the distance between our electrodes, which is known. Inthis exemplary embodiment, an exemplary equation for the impedance ofthe stomach, Z_(s), can be the following:

$Z_{s} = \frac{\ell}{A_{s}\sigma}$

Combining these equations results in the following exemplary equationfor measuring impedance:

$Z = \frac{Z_{t}\ell}{A_{s}\sigma Z_{t}\ell}$

In this exemplary equation, the measured impedance varies with the area,length, and conductivity of the stomach. In this exemplary embodiment,there is an assumption that the impedance of the tissue is constant andthe length is known. By accounting for the changes in the measuredimpedance that are from the changes in conductivity, we can use thisexemplary model to calculate changes in the stomach's area.

FIG. 22A shows an exemplary embodiment of a GRV sensor composed of twoelectrodes, 2208 and 2209, in a bipolar impedance measurementconfiguration. The electrodes of the conductivity sensor may also beganged together form a single electrode for the GRV sensor. In thiscase, FIG. 22A shows a GRV sensor composed of three electrodes,2201-2204, 2208, and 2209, in a tripolar impedance measurementconfiguration. FIG. 22B shows an exemplary embodiment of a GRV sensorcomposed of two electrodes in a bipolar impedance measurementconfiguration. The electrodes of the conductivity sensor be gangedtogether form a single electrode for the GRV sensor. FIG. 22C shows anexemplary embodiment of a GRV sensor composed of two source electrodes,2202 and 2205, and two sense electrodes, 2206 and 2201, in a tetrapolarimpedance measurement configuration. FIG. 22D shows an exemplaryembodiment of a tetrapolar impedance measurement configuration. The fourelectrodes of the conductivity sensor, 2201-2204, are ganged together toform one source electrode for the GRV sensor. The other source electrodeis 2205. The sense electrodes in FIG. 22D are 2206 and 2207. FIG. 22Eshows an embodiment of a GRV sensor composed of four electrodes in atetrapolar impedance measurement configuration. The conductivity sensorin this embodiment is composed of just two electrodes, 2201 and 2202, tosimultaneously inject current and sense voltage forming a bipolarconductivity measurement configuration. For measuring GRV, the sourceelectrodes are 2205 and 2202 and the sense electrodes are 2206 and 2201.These embodiments are only examples and are not intended to limit thescope of this invention. Many other embodiments of electrodes forming aGRV sensor and a conductivity sensor are possible with or without sharedelectrodes and in bipolar, tripolar, or tetrapolar modes.

An exemplary process for utilizing the apparatus described in FIG. 22 isdescribed in FIG. 23 . In the first step of this exemplary process 2301,the clinician connects the feeding tube 102 to the monitor 110. In step2302, the clinician inserts the feeding tube. In step 2303, theclinician locates the feeding tube such that the GRV sensor is locatedin the patient's stomach. In step 2304, the monitor performs a test toensure that the electrodes of the GRV and conductivity sensor are ingood contact with the patient, either by touching tissue, being immersedin conductive fluid like gastric chyme, or a combination of both. Instep 2305, the monitor begins taking GRV measurements to establish abaseline measurement. In step 2306, this baseline measurement can becompared to models to estimate the patient's GRV. The model may acceptthe patient's information such as sex, age, weight, height, etc. to helpmake the impedance measurement from the GRV sensor more accurate. Instep 2307, the monitor takes a conductivity measurement with theconductivity sensor at the distal tip of the feeding tube. Since thedistal tip of feeding tube should be immersed in gastric chyme, theconductivity measurement should reflect just the intrinsic electricalconductivity of the chyme. In step 2308, the clinician measures GRV byaspiration and enters this into the monitor. The clinician may havemeasured the GRV by aspiration prior to inserting this instrumentedfeeding tube. In this case, the clinician may enter the time and datethat the aspirated GRV measurement was taken. Alternatively, the monitormay be able to get this data by data exchange with electronic medicalrecords. In step 2309, the monitor estimates the GRV from model data,the conductivity readings, and previous GRV measurement (aspirated GRVmeasurements or previous reading made by the monitor). Finally, in step2310, the monitor displays the live GRV measurement to clinician. Inaddition to the live GRV estimate, the monitor may also display themonitor's confidence in the live GRV measurement and a trend of theprevious GRV readings.

In an exemplary embodiment, conductivity can be a useful indicator forestimating GRV. In this embodiment, gastric residual volume isdetermined by measuring the conductivity of gastric contents before andafter an injection of a control bolus. In this embodiment, aconductivity sensor is located on the distal tip of the feeding tube.Such a conductivity sensor may be composed of two or more electrodesthat can be connected via wires to the monitor. The monitor 110 can takecontinuous conductivity measurements of the gastric contents. In thisembodiment, a combination of multiple sensors can be used, such as thosesensors disclosed herein and other sensors, and such combinations shouldbe considered within the scope of the various embodiments describedherein. The monitor can then control a known amount of fluid to beintroduced through the feeding tube and into the stomach, which in anexemplary embodiment can be 50 mL of distilled water. Utilizing water asa control can be advantageous, since acute care patients requirehydration and water is a safe substance. The conductivity sensor canthen continually measure the change in conductivity of the gastriccontents after introducing this control bolus of distilled water.

VII. Tube Localization Through Impedance Measurements

An exemplary embodiment for determining feeding tube location is tomeasure the impedance between one or more impedance sensors on thefeeding tube and a reference sensor. The impedance sensors on thefeeding tube 102 may be electrodes. The reference sensor may be anelectrode patch adhered to the skin of the patient about 4finger-breadths (about 4-5 cm) to left of the umbilicus. In thisexemplary embodiment, there are two or more source patches attached tothe skin of the patient between which an alternating current is driven.For example, one source patch may be placed on the right side of thepatient's neck and the other can be placed 1 cm to the left of thereference sensor. These source patches may be electrodes adhered to theskin of the patient. The impedance sensors on the feeding tube, thereference sensor, and the source patches are connected to the monitor.As the feeding tube is inserted down the patient's esophagus, thedistance between impedance sensors on the feeding tube and the referencesensor decreases which causes the measured impedance to also decrease.The impedance between each impedance sensor on the feeding tube and thereference sensor is measured in Ohms by the monitor. Each of thesemeasured impedances may be referred to as a location channel.

The distances between all the impedance sensors on the feeding tube isknown. Differences between the each of these location channels can berelated to the known distances between the impedance sensors. Forexample, a calibration factor can be computed for each location withinthe body and between each pair of two different impedance sensors bydividing the measured difference between two location channels in Ohmsby the distance in centimeter between the impedance sensors associatedwith the two location channels. The calibration factor may changebecause of the anatomical structures around it. When two impedancesensors are in an area with relatively low resistivity, they will have alow difference in their location channels. Similarly, when two impedancesensors are in an area with relatively high resistivity, they will havea higher difference in their location channels. As an example, there maybe highly resistive gas in the patient's stomach. When two electrodespass into this gas the calibration factor between these two electrodeswill increase.

The impedance between the impedance sensors on the feeding tube and thereference sensor may change because of respiration, the patient's heart,beating, or other physiological processes. In this exemplary embodiment,the location channels are filtered and contain only frequencies belowthe heart and breathing rate of the patient. The amount that therespiratory and cardiac rhythms impact the location channels may also beused to indicate location. While the impedance sensors on the feedingtube are near the heart and lungs, the amplitude of the changes in thelocation channels which result from the heart and lungs will be high.Near the diaphragm or within the stomach, the changes in the locationchannels which result from the heart and lungs will be lower. As theclinician inserts the tubes from nose, into esophagus, and into thestomach they will see the amplitudes of cardiac and respiratoryartifacts rise and fall. If they fail to see this characteristicpattern, it may indicate the feeding tube is not in the esophagus butrather in the lower respiratory tract.

The location of the impedance sensor in the patient's body may bemonitored consistently by monitor 110. This location information may beused to detect if the feeding tube is moving throughout time. Thefeeding tube may move up into the esophagus or move too low in thestomach or past the pyloric sphincter. An alarm may sound to detect ifthe feeding tube has moved outside of a preset range. This wouldindicate to a clinician that the position of the feeding tube may needto be adjusted to return it to an appropriate location.

An exemplary process for utilizing the apparatus described is providedin FIG. 24 . In step 2401, patient data, including but not limited toname, ID number, sex, height, and weight can be entered into the monitormanually or through an electronic data interchange. In step 2402, thetarget distance for tube insertion can be calculated. For example, thenomogram proposed by Cirgin Ellett may be utilized to calculate thetarget distance from the patient data entered. In step 2403, the sourcepatches and reference sensors are attached to the patient's skin. Thefeeding tube 102 is inserted partially into the patient in step 2404. Instep 2405, the monitor analyzes the location channel from each of theimpedance sensors on the feeding tube and computes a calibration factor.This calibration factor is used to convert the location channels intounits of distance, such as centimeters. In step 2406, the monitor usesthe conversion factors and respiratory artifacts to determine itslocation relative the lungs, heart, LES, stomach, etc. In step 2407, themonitor calculates a probability that the feeding tube is in the lowerrespiratory track or the stomach from the location channel data,conversion factors, respiratory artifacts, and cardiac artifacts. Instep 2408, the current status of the feeding tube is displayed to theclinician. Step 2409 is reached when the clinician has inserted thefeeding tube a certain distance. This distance may be computed as fromthe patient data input in step 2401, it may be based on the alreadycomputed target distance from step 2402, or it may be a fixed distance.In one exemplary process, this distance is 25 cm. In step 2409, themonitor presents a report which contains summaries or charts of the tubeinsertion progress. The information in the report may include each anumerical read out of the location channels, the calibration factors,the respiratory artifacts, and the cardiac artifacts. Each of thesevariables may be plotted against time and displayed in a chart.Likewise, the monitor may compute an estimated location from all thesevariables. The calibration factors, the respiratory artifacts, and thecardiac artifacts may further be plotted on a chart with respect to theestimated distance. Step 2410 is reached once the targeted insertion isreached. Either automatically or at the prompt of the clinician, themonitor will submit an EMR. In step 2411, the feeding tube is in thestomach and at the targeted distance which signals to a feed pump tostart delivering nutrition.

VIII. Tube Localization Through Local Conductivity Measurements

The conductivity measurement from the conductivity sensor (2201-2204) atthe distal tip of the feeding tube 102 in FIGS. 22A-22E may also be usedto determine feeding tube placement. The conductivity sensor canidentify the tissues that it is in contact with because each tissue hasdifferent conductivity. The conductivity at two or more frequencies maybe measured to further help determine the identity of the tissue. Thelower respiratory tract is filled with air, lined with mucus, andpropped open by connective tissue, namely tracheal cartilage. Air andconnective tissue has low conductivity. Additionally, since the lowerrespiratory tract is propped open by connective tissue, the conductivitysensor may move away from the walls of the trachea or bronchi and onlybe touching air. This effect can be emphasized by placing theconductivity sensor in a depression on the feeding tube. This ensuresthat the conductivity sensor reads the low conductivity of air if it isever in the lower respiratory tract. The esophagus is a virtual spacelined with smooth muscle. While the feeding tube is in the esophagus,the walls will close in around the tube and make electrical contact withthe conductivity sensor. If the conductivity measurement is within therange of smooth muscle tissue, this indicates that the feeding tube islikely in the esophagus. While the feeding tube in is in the stomach,the conductivity sensor will measure the high conductivity of gastricchyme. This high conductivity indicates that the conductivity sensor isplaced in the stomach. The pattern that the conductivity changes throughtime may also be indicative of the tissue touching the conductivitymeter. If the feeding tube was in the lower respiratory tract, thefeeding tube may go in and out of electrical contact with the walls ofthe tract. This may produce a characteristic pattern of conductivityindicative of being in the lungs. Likewise, in the esophagus, themuscles may expand and contract. This will vary the conductivity of themuscles and change the pressure on the conductivity sensor. This mayresult in a conductivity pattern in time that is indicative of being inthe esophagus.

An exemplary process for using the conductivity sensor to assist withtube placement is show in FIG. 25 . In step 2501, the clinician insertsthe feeding tube with a conductivity sensor into the patient. In step2502, the monitor 110 measures the conductivity at one or morefrequencies. In step 2503, the monitor analyzes the conductivity andpattern of conductivity changes. In step 2504, the monitor correlatesthese conductivity values and patterns to the expected conductivity andconductivity patterns of different tissues a feeding tube may come intocontact during regular or erroneous use. In step 2505, the monitorcalculates that probability that the conductivity sensor is touching aparticular tissue. Finally, in step 2506, the monitor displays theconductivity information and the detected tissue to the clinician. Ifthe monitor detects that the conductivity sensor is in the lowerrespiratory tract with a probability above a certain threshold, it willalert the clinician to remove the feeding tube and try to insert itagain.

FIG. 26 shows an embodiment of the GRV measuring device in a humanstomach. GRV measuring device 2608 in this embodiment is a catheter, ortube containing at least one lumen. The GRV measuring device alsoincludes sensor or sensors 2610, in this embodiment, at or near thedistal tip of the GRV measuring device. The lumen may be used forfeeding the patient, and/or introducing a GRV indicator into stomach2602. Stomach contents 2604 include gastric secretions, nutrients whichwere previously present in the stomach, nutrients that have been addedto the stomach via the GRV measuring device or otherwise, as well as anyGRV indicators used to determine the GRV of the stomach.

GRV indicators may include a substance at a higher or lower temperaturethan the stomach contents, a substance at a higher or lower pH than thestomach contents, a substance at a higher or lower O2 concentration thanthe stomach contents, a substance at a higher or lower CO2 concentrationthan the stomach contents, a substance at a higher or lower ion (such asMagnesium) concentration than the stomach contents, a substance at ahigher or lower glucose concentration than the stomach contents, asubstance at a higher or lower viscosity than the stomach contents, etc.Additional GRV and/or stomach entry indicators include electricalproperties (conductance, resistance, current generation based on theacid level, impedance, etc.) that will increase or decrease depending onthe ratio of stomach acid to tube feed in the stomach. Other GRVindicators are also possible and some are described in other embodimentsherein.

GRV indicators may be introduced through the lumen of GRV measuringdevice 2608 into stomach contents 2604. Sensor or sensors 2610 then canmeasure the change in properties of the stomach contents to determinethe Gastric Residual Volume, or GRV, of the stomach.

For example, if a substance is introduced into the stomach which is at ahigher or lower temperature than the stomach contents, the sensor(s) canmeasure the magnitude of change, and/or the rate of change oftemperature of the stomach contents to determine the GRV. Both the rateof initial change, and the rate of change back to the pre-introductionstate can be measured, as well as the magnitude of change. In general,the change from the maximum change, back to the pre-introduction level,is a slower change and easier to measure, but either change can bemeasured. After the GRV indicator is introduced, and the maximum levelof the GRV indicator has been measured, the rate of change of theindicator, or slope of the temperature vs. time curve, can be measured.A relatively steep slope indicates a higher GRV, where a relativelyshallow slope indicates a lower GRV. The same can be done withconcentration and other GRV indicator types. For example, if the GRVindicator is glucose, the sensor(s) would measure the concentration ofglucose within the stomach contents and the change in concentration overtime.

Alternatively, a bolus of a substance at a fixed temperature (orconcentration, etc., depending on the GRV indicator) can be introducedinto the stomach and the temperature (or concentration, etc.) of thestomach contents can be measured as soon as the contents have had achance to mix. The relatively immediate magnitude of change intemperature or concentration may also be an indicator of the GRV of thestomach. The lower the GRV, the greater the impact the introduction ofthe GRV indicator will have on the stomach contents. The higher the GRV,the lower the impact will be, resulting in a lower magnitude of measuredchange of the GRV indicator.

Another embodiment of the GRV measuring device includes a temperaturechanging mechanism as part of the device. In this embodiment, thetemperature of the stomach contents may be altered by either a heatingor cooling element. For example, GRV measuring device 2608 may include aheating element (not shown) which heats the contents of the stomach. Thechange of temperature is measured over time and the rate and/ormagnitude of the temperature change as the stomach contents heat and/orcool can be used to determine the GRV of the stomach.

Another variation of this embodiment of the GRV measuring devicemeasured pH instead of temperature. A substance of a certain pH (higheror lower than that of the stomach contents) can be introduced into thestomach, and the change in pH measured over time to determine the GRV ofthe stomach.

A controller (not shown) may be used as part of the GRV measuring deviceto record and/or interpret the various levels of GRV indicator(s)measured by sensors within the stomach. The controller may also use theGRV info to control feeding volume/rate/frequency/contents.

FIG. 27 shows a stomach into which a substance containing aconcentration of a GRV indicator is introduced and the concentrationmeasured over time within the stomach contents. In this embodiment, thesensor(s) measure concentration instead of temperature. For example, GRVindicator 2702 in this embodiment may be glucose, or magnesium, or anyother suitable substance, the concentration of which can be measured.

FIG. 28 shows a graph of the temperature of the stomach contents overtime as sensed by the sensor(s) and recorded and/or interpreted by thecontroller after a bolus of cold liquid is introduced into the stomach.The magnitude of the temperature drop and the slope of the gradualtemperature rise back to normal can be used either together, orseparately, to determine the GRV of the stomach.

FIG. 29 shows a similar graph for the introduction of a GRV indicatorfor which the concentration or pH is measured. After introduction of theGRV indicator into the stomach, the concentration or pH rises, and thengradually returns to normal over time. Again, the magnitude of thechange and the slope of the return to normal of the concentration or pHof the GRV indicator within the stomach can be used together, orseparately, to determine the GRV of the stomach.

FIG. 30 shows a graph of the temperature of the stomach contents overtime as sensed by the sensor(s) and recorded and/or interpreted by thecontroller after multiple boluses of cold liquid are introduced into thestomach. Note that in this example, the magnitude and/or slope of thegraph after each bolus may be utilized by the controller, in addition tothe overall magnitude and slope of the boluses combined. Multipleboluses may be used with other GRV indicators as well.

FIG. 31 shows an embodiment of the GRV measuring device where sensors3102 are outside of the stomach, and preferably outside the patient'sbody. This embodiment is limited to GRV indicators which can travelthrough tissue such as temperature, radiation, sound waves, magneticsubstances, etc.

FIG. 32 shows an embodiment of the GRV measuring device where sensors3202 are located along the length of the catheter or tube. In thisembodiment, the GRV indicator can be measured at different locationswithin the stomach, providing more information regarding the GRV. Forexample, assuming the patient is upright and the stomach contents are atthe bottom of the stomach, the GRV indicator readings at the moreproximal end of the GRV measuring device would be much lower, or evennull, where the measurements at the distal end of the device wouldchange over time as the GRV indicator is introduced and diluted by thestomach contents. Depending on the different GRV indicator measurementsat different locations along the GRV measuring device, more informationcan be obtained about the volume of the contents in the stomach. Forexample the device may be able to determine that the stomach isapproximately half full etc.

FIGS. 33 and 34 show embodiments of the GRV measuring device where thesensor(s) are at different location. FIG. 33 shows sensor(s) 3302 on theoutside of tube/catheter. Note that in any of the embodiments herein thesensor(s) may run radially around the tube/catheter or be on one or moresides of the catheter/tube. This, and other embodiments, also allows fora separate feeding tube to be inserted through the GRV measuring device(not shown). This may be desirable where a standard feeding tube isbeing used. Also, it is possible to insert the GRV measuring device intothe patient over a feeding tube that is already in place. This would beadvantageous when it is not known at the time of placement of thefeeding tube that the GRV measuring device will be used.

FIG. 34 shows sensor(s) 3402 embedded in the wall of the GRV measuringdevice. This embodiment offers the advantage of a smooth transition onboth the outside and the inside of the GRV measuring device. Note thatthe sensor(s) in any of the embodiments may be at any location along thelength of the GRV measuring device.

FIG. 35 shows an embodiment of the GRV measuring device which isseparate from the feeding tube. In this embodiment, feeding tube 3506may be inserted into the patient separately from GRV measuring device3502. GRV measuring device in this embodiment may or may not have alumen. Since the feeding of the patient occurs through a separate tube,the size of the GRV measuring device can be much smaller and be insertedalongside of the feeding tube. In fact, GRV measuring device in thisembodiment may be similar dimensions to a guide wire (down to 0.5 mm orless, or 1.0 mm or less, or 2.0 mm or less) with sensor(s) 3504 at itsdistal end or along its length. In this embodiment the GRV indicator maybe introduced through the separate feeding tube.

FIG. 36 shows a GRV measuring device similar to that of FIG. 35 ,however in this figure, the GRV measuring device is inserted through thefeeding tube. This configuration has the advantage of easily beinginserted after the feeding tube is already in place. In this and any ofthe embodiments the GRV measuring device may be introduced onlyperiodically before or after the GRV indicator is introduced into thestomach. In this way, the extra bulk of the GRV measuring device doesnot significantly interfere with the feeding process through the feedingtube. Alternatively, the GRV measuring device may be small enough to notadversely impact the flow of nutrients or other substances through thefeeding tube.

FIGS. 37 and 38 illustrate how the sensor(s) of the GRV measuring devicemay be placed at various places relative to the feeding tube. This mayhelp obtain cleaner measurements after introduction of the GRVindicator. For example, if a heated substance is introduced through thefeeding tube, it may be advantageous to have the sensors of the GRVmeasuring device some distance away from the exit of the feeding tube,both to protect the sensors from extreme heat, but also to get a cleanertemperature reading. More mixing of stomach contents will have occurredthe further from the source of the GRV indicator introduction thesensor(s) are.

Alternatively the sensors may be placed within the feeding tube when theGRV indicator is introduced through the feeding tube to obtain abaseline reading of the temperature/concentration/pH etc. of the GRVindicator. The sensors may then be moved into the stomach contents toobtain the changing readings which will be used to determine GRV.Alternatively, the GRV measuring device may have sensors along itslength to achieve the same thing. There may be other advantages tomoving the GRV measuring device during the measurement process.Measuring the GRV indicator at different places within the stomachand/or stomach contents will provide more information about the stomachcontents.

FIG. 38 shows sensor(s) 3802 of the GRV measuring device in the pylorus3804. In this embodiment, the stomach content volume is estimatedthrough direct measurement of the input volume (enteral feedingmaterial) and output volume (pylorus transit). The amount of materialentering and passing through the pylorus may be measured with avolumetric flow meter, or Doppler ultrasound, or optics, or any othersuitable technology. In one embodiment, after magnetic materials areintroduced into the stomach, the movement of the materials induces acurrent as it passes the pylorus transit which can be measured eitherwithin the pylorus, or outside of the patient.

Note that in any of the embodiments herein, the GRV measuring device maybe outside of, inside of, incorporated into or completely separate fromthe feeding tube.

Other embodiments of the invention are shown in FIGS. 39-41 . In theseembodiments, the GRV measurement device is also used to locate thedevice, or a feeding tube, within the stomach to ensure proper feedingand GRV measurements. In these embodiments transmitters 3902 give offsignal 3904 which is detected by location receivers 3906. Thetransmitters may be separate from the sensor(s) shown in otherembodiments, however both may be present on the GRV measuring device(note that the sensor(s) are not shown in FIGS. 39-41 ). The locationreceivers may exist outside the body as shown in FIGS. 39 and 40 , orthey may be part of the GRV measuring device, as shown in FIG. 41 . Thetransmitted signal may be a sound signal, an ultrasound signal, apressure signal, or any other suitable signal. Alternatively, or inaddition, pH, temperature, or any of the GRV indicator signals may beused. The location receivers receive the signal either through thetissue, as shown in FIGS. 39 and 40 , or after reflected signal 4102 hasbounced off of the walls of the stomach and possibly the stomachcontents, as shown in FIG. 41 . The embodiment of the GRV measuringdevice in FIG. 41 includes both the transmitters and the locationreceivers on the device within the stomach.

FIGS. 39 and 40 show the transmitter in the empty part of the stomachand in the stomach contents, respectively. The signal received when thetransmitter is in these two different locations will be very different,and will aid in locating the tip of the feeding tube. The transmittersmay be at the tip of the feeding tube, and/or may be elsewhere relativeto the tip of the feeding tube.

FIGS. 42 and 43 show embodiments of the GRV measuring device being usedpercutaneously. For example, the GRV measuring device can be used as, orin conjunction with, a Percutaneous Endoscopic Gastrostomy, or PEG,tube. In this situation the feeding tube goes through the abdomen of thepatient, directly into the stomach, to feed the patient. Shown here isPEG tube 4202 going through skin 4208, fat 4206 and muscle 4204 andthrough the stomach wall so that the tip of the PEG tube is in thestomach. The GRV measuring device may be incorporated into the PEG tube,or may be separate as shown here. GRV measuring device 4212 is shownhere being used through the inside of a PEG tube. In this and otherembodiments the GRV measuring device is connected to a controller torecord and/or interpret the measurements sensed by the sensors.

In this and other embodiments, GRV measuring device may be in thestomach throughout feeding, or it may be introduced periodically whenmeasurements are desired. Restrictor 4210 may be used to control theflow of nutrients into the stomach. The restrictor may be controlled bythe controller in a feedback loop so that nutrients are only introducedwhen the GRV is at or below a certain level. Nutrients may also beautomatically limited when the GRV is at or above a certain level. Theselevels may be preset, or may be set by the controller and can beadjusted as necessary. This type of feedback control also allows forbolus feeding vs. continuous feeding which is more physiologicallyrepresentative.

FIG. 43 is similar to FIG. 42 except that the entrance point for the GRVmeasuring device is between the patient and the resistor. This allowsthe resistor to be more easily used when the GRV measuring device is inplace.

Note that the embodiments in FIGS. 42 and 43 can be used with a standardPEG tube. Alternatively, the GRV measuring device may be incorporatedinto a PEG tube.

FIG. 44 shows an embodiment of the GRV measuring device for use with ajejunostomy tube. In this embodiment the feeding tube enters theintestines rather than the stomach. Similar to other embodiments herein,the GRV measuring device may be used with a standard jejunostomy tube,or may be incorporated into a jejunostomy tube.

FIGS. 45-49 show detailed embodiments of the GRV measuring device. FIG.45 shows an embodiment of the GRV measuring device which is incorporatedinto a feeding tube. Device shaft 4502 includes sensor or sensors 4504,measurement communication line 4506, which may be a metal wire, as wellas feeding lumen 4508. Sensor(s) 4504 measure the temperature, pH,concentration etc. of the GRV indicator in the stomach after theindicator is introduced through the device or created by the device. Forexample, a fluid below body temperature may be introduced into thestomach through lumen 4508. The magnitude of the change of temperaturewithin the stomach is measured by sensor(s) 4504, as well as the rate ofreturn to normal temperature. This information is transferred alongcommunication line 4506, along shaft 4502 back to the controller. Thecontroller may control the feed supply either with user input, orautomatically, depending on the gastric volume analysis of thecontroller.

Note that sensor(s) 4504 may be placed anywhere along the length of thedevice. Also note that sensor(s) may be placed on either the inside ofthe device (within lumen 4508) or on the outside, or both. Havingseparate sensors on both the inside and outside of the device may allowmeasurements of the untainted GRV indicator as it is entering thestomach (inside sensors) as well as measurements of the change in theGRV indicator over time (outside sensors). These sensors may be the samesensor, where it measures both inside the device, and outside thedevice. Also note that there may be a barrier or insulator between thesensor and either the inside of the device, or the outside of thedevice. This would allow the sensor to measure the GRV indicator oneither the inside of the device or the outside of the device withoutbeing tainted.

Alternatively the GRV measuring device may cause a cooling of thestomach contents with a cooling element (not shown) on the device, andmeasure the resulting magnitude and rate of temperature change todetermine gastric volume.

In another example, the pH of the stomach contents may be measured todetermine gastric volume. A substance of a known pH (which may be onlythe feeding substance itself) is introduced into the stomach, and thesensor(s) measure the change in pH and the rate of return to normal pH,send the information back to the controller, and the controller can thendetermine gastric volume.

In another embodiment, the GRV measuring device may use more than oneGRV indicator. For example, both temperature and pH may be used. In thisexample, measurement of one GRV indicator may be used to confirm themeasurement of the other GRV indicator for a more accurate result. Inaddition, the measurements may be taken at different locations to assurestomach content mixing and/or to improve accuracy. Other GRV indicatorsmay be combined in a similar manner.

FIG. 46 shows another embodiment of the GRV measuring device. Thisembodiment is designed to be used with a feeding tube, either alongsideit or through the lumen of a feeding tube. This embodiment may be of arelatively small diameter (down to 0.5 mm or less, or 1.0 mm or less, or2.0 mm or less) so that it does not substantially impede the flow ofnutrients to the patient through the feeding tube, or is not difficultto insert into the patient alongside a feeding tube. Shaft 4602 ispreferably relatively stiff, similar to a guidewire, and incorporatesthe signal communication from sensor(s) 4604. Shaft 4602 may be made outof metal such as stainless steel or other appropriate material. In thisembodiment, the GRV indicator may be introduced through the separatefeeding tube. Note that this and other embodiments may be placed intothe stomach before or after the feeding tube is placed in the stomach.

FIGS. 47-49 show another embodiment of the GRV measuring device whichcan be used in conjunction with a feeding tube after the feeding tube isalready inserted. This embodiment is designed to go on the outside of afeeding tube and includes relatively stiff shaft 4708, sheath 4704,sensor(s) 4702 and slit 4706. Shaft 4708 may be made out of similarmaterials to shaft 4602 in FIG. 46 . Sheath 4704 is preferably thinenough so that it can easily be slid over a feeding tube, yet rigidenough so that it does not collapse. Various polymers and othermaterials may be used. To introduce this embodiment after a feeding tubeis already in place, sheath 4704 is placed over the outside of theproximal end of the feeding tube using slit 4706. The GRV measuringdevice is then slid down the outside of the feeding tube into thestomach of the patient using the relatively rigid shaft 4708.

FIG. 48 shows this embodiment of the GRV measuring device after it isplaced over feeding tube 4802.

FIG. 49 is a cross sectional view of this embodiment of the GRVmeasuring device.

FIG. 50 shows an embodiment of the device where GRV and entry in thestomach is based on a continuously or intermittently monitored physicalcharacteristic. In this embodiment, the GRV indicator may be inherent inthe feed or meal itself, with no additives required. In this embodiment,the GRV indicator may be a physical characteristic such as pH orelectrical resistance, impedance or conductance. In this embodiment, thephysical characteristic may be monitored over time and the changes thatoccur as the meal empties from the stomach may be recorded. As the mealleaves the stomach and the relative concentration of gastric fluidincreases the physical characteristic is altered in a measureable way.In one embodiment, the physical characteristic is pH wherein the pHdecreases as the meal leaves the stomach and the gastric secretionsrepresent more of what is left in the stomach. Once the pH reaches asufficiently low level the device may alert the user that the meal hasleft the stomach and the patient is ready for another bolus. In anotherembodiment the physical characteristic is resistance or impedance. Themeal delivered to the patient may be formulated to have high resistanceor impedance so that subsequent decreases will indicate increasingconcentration of gastric secretions. The opposite is true ofconductance, which may increase as the meal leaves the stomach.

In yet another embodiment, the sensor may consist of a circuit that ispowered by acid. For example, two leads may be introduced into thestomach consisting of different metals (in the preferred embodimentthese are copper and magnesium) In the presence of acid, these metalsact like the terminals of a battery and create a current. This currentcan be continuously or intermittently recorded and report the emptyingof the stomach based on the increased concentration of acid. The sameelectrodes may also be used to sense the electrical parameters(impedance, conductance, resistance. Etc.) of the stomach to providefurther information to help increase the sensitivity and specificity ofthe measurement. Each of these measurements of the physicalcharacteristics of the stomach may be used, alone or in combination, toreport that the sensor (and therefore the tube or catheter tip) is inthe stomach and not in the lung. Ideally two or more parameters aremeasured (pH, current due to acid, impedance/conductance, etc.) toimprove the accuracy of the measurement. This is important as theincidence of tube placement in the lung is as high as 20% and startingtube feeds with the tip in the lung can be fatal. In this embodiment,the sensors may be incorporated into the catheter/tube itself or may bea separate component that is threaded down the inside of an existingfeeding catheter/tube to provide a spot reading as to the location ofthe tip of the tube. In the ideal embodiment, the sensor(s) is/areintegrated into the catheter/tube to first provide an indication thatthe catheter/tube is in the stomach (and not the lung) and then providea signal to indicate the GRV to help optimize feeding. In the idealembodiment, as well, the feeding may be accomplished via a closed loopsystem that will automatically detect the GRV and deliver tube feed whenappropriate based on the programmed nutritional goals for each patient.In this embodiment, target volumes of tube feed may be set per period oftime and maximum volumes may be programmed.

FIG. 50 shows a patient with GRV measuring device 5006 placed in stomach5002. Note the proximity of lungs 5004 and why it is important to beable to confirm placement of the GRV measuring device in the stomach,rather than the lungs. The GRV is measured as discussed herein.Controller 5008 may intermittently or continuously track the GRV viaconnector 5010 and using this information, control the feeding of thepatient via valve or restrictor 5014 using connector 5012. Note that theconnectors may be wired, as shown here, or wireless. Feed supply 5016 isconnected to the feeding tube and the volume, rate, frequency, andcontent of the feed is controlled by controller 5008. GRV indicators maybe inherent in the feed, added to the feed, or added independently ofthe feed. The controller may collect measurements of the GRV indicatorinside the feeding tube, just before the feed is released into thestomach, as well as within the stomach contents over time. This providesthe controller with a reading of the GRV indicator just before mixingbegins, to provide an accurate GRV.

FIG. 51 shows an embodiment of the GRV measuring device which uses thegastric acid in the stomach to create a sort of battery which creates ameasurable current which is measured and analyzed by a controller. Themeasured current is indicative of the GRV in the stomach. GRV measuringdevice shaft 5102 contains wires 5108 and 5110 which connect to twodifferent electrodes, 5106 and 5104. The electrodes in this embodimentare made from dissimilar metals, such as Aluminum and Copper, but otherdissimilar metals may be used. The current between the two electrodes issensed by current sense resister 5112. In this embodiment, current isgenerated by the fluid in the stomach, and measured and analyzed by thecontroller to determine GRV.

In an alternative embodiment, the impedance of the stomach fluid ismeasured instead of current. The impedance is indicative of the ratio ofgastric acid to feed, providing an estimate of GRV. This embodimentwould look similar to the embodiment shown in FIG. 51 except that theelectrodes would preferably be of the same metal rather than dissimilarmetals. The controller would generate a voltage and measure theresulting current to determine the impedance of the fluid in thestomach. In this embodiment, voltage is generated by the controller, andcurrent is passed through the fluid in the stomach and the resistance ismeasured and analyzed by the controller to determine GRV.

Using the different electrical properties of the gastric acid in thestomach and the feed, GRV can be estimated by conductivity, current,impedance, capacitance, electrical resistance etc. AC and/or DC signalscan be used to make these measurements. Several possible embodiments areenvisioned. For example:

In one embodiment, an additive liquid element (such as water, saline orsimilar) is introduced by the source that is significantly lower orsignificantly greater in temperature then the nominal contenttemperature. Measurement of the temperature may be recorded by sensorsin one or more locations in the content mixture. In one embodiment, therate of change in temperature over a period of time indicates thegastric volume. In one embodiment, the resulting temperature from themixture after a set period of time indicates the gastric volume. In oneembodiment, a physical thermal element introduces a sudden temperaturechange. This element quickly could heat or chill the gastric contents incontact with the element.

In one embodiment, an additive element is introduced that changes theviscosity of the contents. The resulting change in viscosity indicatesthe gastric volume. In one embodiment, the additive component glucose isintroduced. The resulting change in concentration of glucose indicatesthe gastric volume. In one embodiment, coloring elements such asmethylene blue is introduced and the resulting concentration is used toindicate gastric volume. In one embodiment, an additive component isintroduced that changes the pH value of the gastric contents. The rateof change or resulting pH value indicates gastric volume. In oneembodiment, an additive element is introduced that changes theconductivity of the contents. In one embodiment, an additive element isintroduced that changes the refractive index, opacity, absorptivity,luminosity or color of the contents. In one embodiment, an additiveelement is introduced that changes the specific gravity of the contents.

In one embodiment, an additive component is introduced that causes thecontents to change and is measure through a method of titration. In oneembodiment, the additive component causes contents to solidify. In oneembodiment, the additive component causes contents to changeconductivity. In one embodiment, the additive component causes contentsto change optical opacity or color.

In one embodiment, pressure is introduced by introducing additionalmaterial into the gastric space. This material may be air, saline,water, or other. In one embodiment, pressure may be introduced byinflation of a balloon. In one embodiment, pressure response is measuredinternally. In one embodiment, pressure is measured externally withpressure gauges around the abdomen. This pressure difference before andafter introduction will indicate volume.

In one embodiment, an acoustic source is used to produce standing wavesin the gastric space. The resulting pattern of pressure indicates thedimensions of the media, in this case the gastric contents. In oneembodiment, the acoustic source is external and an acoustic or pressuresensors are used internally. In one embodiment, both the source andsensors are internal. In one embodiment, the source is internal and thepressure or acoustic signature can be measured externally. In oneembodiment, both the source and the sensor are external. The acousticsource may be a point source or an array of transducers that produce arange of frequencies and amplitudes. The acoustic or pressure sensor maybe a single point of measurement or an array of sensors.

In one embodiment, the flow rate of material is measured directly in thepylorus transit. The stomach content volume is estimated through directmeasurement of the input (enteral feeding material) and output (pylorustransit). In one embodiment, the amount of material entering and passingthrough the pylorus is measured with a volumetric flow meter. In oneembodiment, Doppler ultrasound is used to measure fluid movement rate.In one embodiment, after magnetic materials are introduced into thestomach, the movement of the materials induces a current as it passesthe pylorus transit. In one embodiment, optics are used to measure flowrate.

In one embodiment, an autonomous device travels within the gastric spaceto ensure all of the gastric contents are aspirated.

Example of Data Processing System

FIG. 52 is a block diagram of a data processing system, which may beused with any embodiment of the invention. For example, the system 5200may be used as part of a controller/monitor disclosed herein. Note thatwhile FIG. 52 illustrates various components of a computer system, it isnot intended to represent any particular architecture or manner ofinterconnecting the components; as such details are not germane to thepresent invention. It will also be appreciated that network computers,handheld computers, mobile devices, tablets, cell phones and other dataprocessing systems which have fewer components or perhaps morecomponents may also be used with the present invention.

As shown in FIG. 52 , the computer system 5200, which is a form of adata processing system, includes a bus or interconnect 5202 which iscoupled to one or more microprocessors 5203 and a ROM 5207, a volatileRAM 5205, and a non-volatile memory 5206. The microprocessor 5203 iscoupled to cache memory 5204. The bus 5202 interconnects these variouscomponents together and also interconnects these components 5203, 5207,5205, and 5206 to a display controller and display device 5208, as wellas to input/output (I/O) devices 5210, which may be mice, keyboards,modems, network interfaces, printers, and other devices which arewell-known in the art.

Typically, the input/output devices 5210 are coupled to the systemthrough input/output controllers 5209. The volatile RAM 5205 istypically implemented as dynamic RAM (DRAM) which requires powercontinuously in order to refresh or maintain the data in the memory. Thenon-volatile memory 5206 is typically a magnetic hard drive, a magneticoptical drive, an optical drive, or a DVD RAM or other type of memorysystem which maintains data even after power is removed from the system.Typically, the non-volatile memory will also be a random access memory,although this is not required.

While FIG. 52 shows that the non-volatile memory is a local devicecoupled directly to the rest of the components in the data processingsystem, the present invention may utilize a non-volatile memory which isremote from the system; such as, a network storage device which iscoupled to the data processing system through a network interface suchas a modem or Ethernet interface. The bus 5202 may include one or morebuses connected to each other through various bridges, controllers,and/or adapters, as is well-known in the art. In one embodiment, the I/Ocontroller 5209 includes a USB (Universal Serial Bus) adapter forcontrolling USB peripherals. Alternatively, I/O controller 5209 mayinclude an IEEE-1394 adapter, also known as FireWire adapter, forcontrolling FireWire devices.

Some portions of the preceding detailed descriptions have been presentedin terms of algorithms and symbolic representations of operations ondata bits within a computer memory. These algorithmic descriptions andrepresentations are the ways used by those skilled in the dataprocessing arts to most effectively convey the substance of their workto others skilled in the art. An algorithm is here, and generally,conceived to be a self-consistent sequence of operations leading to adesired result. The operations are those requiring physicalmanipulations of physical quantities.

It should be borne in mind, however, that all of these and similar termsare to be associated with the appropriate physical quantities and aremerely convenient labels applied to these quantities. Unlessspecifically stated otherwise as apparent from the above discussion, itis appreciated that throughout the description, discussions utilizingterms such as those set forth in the claims below, refer to the actionand processes of a computer system, or similar electronic computingdevice, that manipulates and transforms data represented as physical(electronic) quantities within the computer system's registers andmemories into other data similarly represented as physical quantitieswithin the computer system memories or registers or other suchinformation storage, transmission or display devices.

The techniques shown in the figures can be implemented using code anddata stored and executed on one or more electronic devices. Suchelectronic devices store and communicate (internally and/or with otherelectronic devices over a network) code and data using computer-readablemedia, such as non-transitory computer-readable storage media (e.g.,magnetic disks; optical disks; random access memory; read only memory;flash memory devices; phase-change memory) and transitorycomputer-readable transmission media (e.g., electrical, optical,acoustical or other form of propagated signals—such as carrier waves,infrared signals, digital signals).

The processes or methods depicted in the preceding figures may beperformed by processing logic that comprises hardware (e.g. circuitry,dedicated logic, etc.), firmware, software (e.g., embodied on anon-transitory computer readable medium), or a combination of both.Although the processes or methods are described above in terms of somesequential operations, it should be appreciated that some of theoperations described may be performed in a different order. Moreover,some operations may be performed in parallel rather than sequentially.

FIGS. 53 and 54 show embodiments of the GRV measuring device whichensure accurate gastric tube placement and measure and report gastricresidual volume by measuring the electrical conductivity of therespiratory and gastric systems. Placement in the respiratory systemindicates improper placement and signals the user to replace the device.

Various tissues and fluids have different conductivities, which islargely based on the concentration of ions. Acidic solutions, such asgastric acid, have a large concentration of ions, and thus are veryconductive. Common nutrition that is delivered through gastric tubes,such as milk or Ensure, are only slightly acidic, and thus are onlyslightly conductive.

Conductivity may be measured by passing an alternating current (AC)through the material and measuring voltage. Using Ohm's Law, theconductivity may then be calculated. The frequency of the AC current maybe varied depending on the conductivity of the solution. Higherfrequencies may be used for high conductivity measurements in order tominimize polarization effects (ions migrate towards the poles and blockthe measurement). Lower frequencies may be used for low conductivitymeasurements in order to minimize the effects of cable capacitance(power loss in the cable).

Electrical Conductivity Meters, such as HM Digital AP-2 AquaPro WaterQuality Electrical Conductivity Tester or HM Digital EC-3 ElectricalConductivity Tester, may be used to measure conductivity.

FIG. 53 shows an embodiment of a GRV measuring device which measuresconductance. Catheter 5302 also serves as a feeding tube, with openings5308 through which the feed and/or GRV indicator may flow. Only thedistal end of the catheter/feeding tube is shown here. Distal electrodes5304 measure conductance. Proximal electrodes 5312 also measureconductance. One set, two sets, or more sets of conductance electrodesmay be present along the catheter. Electrical connections, such aswires, pass from the electrodes, through the length of the catheter, tothe proximal end (not shown) and ultimately to a conductivity meter. pHsensor or sensors, 5310 may also be present on the catheter, to aid inthe placement of the catheter and the measurement of GRV.

FIG. 54 shows an embodiment of a GRV measuring device which measuresconductance. Catheter/wire/elongated member 5402 is designed to be usedthrough, or alongside, a feeding tube. Only the distal end of the memberis shown here. Distal electrodes 5404 measure conductance. Proximalelectrodes 5412 also measure conductance. One set, two sets, or moresets of conductance electrodes may be present along the member.Electrical connections, such as wires, pass from the electrodes, throughthe length of the member, to the proximal end (not shown) and ultimatelyto a conductivity meter. pH sensor or sensors, 5410 may also be presenton the member, to aid in the placement of the member and/or feeding tubeand the measurement of GRV.

The pH sensors, or electrodes, may consist of an internal reference andan external facing electrode. The conductance electrodes preferablyexist in pairs, since one is the outgoing signal and the other is theincoming signal. Several pairs may exist on a GRV measuring device. Two“pairs” of electrodes may consist of only 3 electrodes, where oneelectrode serves each “pair”. For example, electrodes 1 and 2 could beused for the first pair, and 2 and 3 can be used for the second pair.Examples of types of pH electrodes which may be used include antimony,glass, and/or ISFET (ion-sensitive field-effect transistor) pHelectrodes.

The length of the GRV measuring device may be from about 25 inches toabout 40 inches. The outer diameter of the GRV measuring device mayrange from about 0.02 inches to about 0.20 inches The GRV measuringdevice may be made out of any suitable material, including polymers,silicone etc. The GRV measuring device may contain one, two or morelumens, which may be concentric or side by side, to accommodate thevarious lumens and electronics required. In some embodiments of the GRVmeasuring device the electrode pairs are located 6 inches from eachother, however the electrodes may be closer, or farther, from eachother.

Below is a table which shows the results of measuring the conductance ofwater, simulated gastric acid and Ensure Plus, a common feed. It can beseen that the conductivity of gastric acid is well above theconductivity of water and Ensure Plus.

Water Sim. Gastric Acid Ensure Plus Conductivity 55 μs 8000 μs 589 μs

FIG. 55 shows that conductivity increases as the percentage of gastricacid increases in various media.

Similar results have been found in the digestive system and respiratorysystem of a pig. See table below. This shows that conductivity can beused to determine placement of the GRV measuring device and/or a feedingtube.

Insertion Length Conductivity (uS) Stomach 27 in 4699 23 in 2994 19 in2975 16.5 in 2845 Lungs 27 in 3385 19 in 3798 16.5 in 2867

FIG. 56 shows pH and conductivity in various anatomical locations in apig. This graph shows that using the combination of conductivity and pHincreases the ability to identify the location of the sensors. Forexample, the pH of the esophagus and the pH of the lungs are similarhere. However the pH of the esophagus or the lungs is very differentthan the pH of the stomach. The conductivity of the esophagus isdifferent than that of the lungs. By using both the pH and theconductivity measurements in any given location, and/or the change ofthe pH and the conductivity measurements in any given location, thelocation of the sensors on the GRV measuring device can be determined.This allows the user to identify when the GRV measuring device is in thelungs by accident, in the esophagus, or in the stomach.

FIGS. 57 and 58 show conductivity and oscillations of conductivity invarious locations in the anatomy of a human before and after feeding.

The human subject was initially in a fasting state. The GRV measuringdevice was inserted into the esophagus, and then into the stomach. Thesubject was fed almond milk three times over two hours, and conductivitymeasurements were taken throughout the experiment. The results are shownin FIG. 57

The conductivity in air is 0 μs, and as the GRM measuring device wasinserted into the esophagus, the conductivity increased significantly.Once the device entered the stomach, the conductivity increased further.FIG. 57 shows that the conductivity drops after every feeding, and thenrises again as the liquid is digested.

FIG. 58 shows a portion of the graph shown in FIG. 57 which has beenmagnified. The data was recorded at a sample rate of 1 Hz (1 reading persecond). The increased resolution in this graph reveals twenty secondoscillations that may be related to the peristaltic motion of theesophagus, stomach, and intestines. The amplitude of the oscillations isplotted at the bottom of the graph in FIG. 57 . When the stomach isfilled, the magnitude of the oscillations is diminished. Once the mealis diluted with gastric acid and the conductivity increases, themagnitude of the oscillations increases. Then as the meal is digested,the magnitude of the oscillations again decreases. FIG. 57 shows thistrend, since the oscillation range increases before feedings, and thendecreases after feeding. The location of the GRV measuring device andGRV may be measured by measuring conductivity, and/or the magnitude ofconductivity oscillations.

FIGS. 59 and 60 show pH and oscillations of pH while the GRV measuringdevice is being moved from the esophagus to the stomach of a fastinghuman.

The GRV measuring device was inserted from the esophagus into thestomach. The measured pH decreases when the stomach is entered.

FIG. 60 shows a portion of the graph shown in FIG. 59 which has beenmagnified. The pH measurements are shown to oscillate similar to thoseof the conductivity measurements.

FIG. 61 shows both conductivity and pH measurements from the GRVmeasuring device during feeding. At feeding, the pH rises. Theconductivity simultaneously drops and variability among sensorsdecreases. Although not visible in this graph, as digestion occurs andthe stomach empties, pH decreases and conductivity rises. Variability inmeasurements is lower when the stomach is full due to the homogenouscontents of the stomach. As food is digested, variability increases asperistaltic motions increase, and as the sensors move between areas ofliquid and pockets of air.

By measuring both pH and conductivity, an algorithm that accounts forthe mean and variability of pH and conductivity can be used to detectthe various stages of digestion.

For example, food percentage during feeding can be calculated byapplying empirically measured functions of ph and conductivity vs food %(food/(food+gastric fluid)).

With a known volume of a known type of food delivered at any given time,the contents before and after feeding can be calculated:

VolBefore*FoodPercentBefore+FeedVol=VolAfter*FoodPercentAfter

Immediately before and after feeding, the following must be true:

VolAfter=VolBefore+FeedVol

Therefore, the initial equation can be written:

VolBefore*FoodPercentBefore+FeedVol=(VolBefore+FeedVol)*FoodPercentAfter

And this equation can be written as an equation in which we have all theinformation needed to calculate the volume prior to feeding:

VolBefore=FeedVol*((FoodPercentAfter−1)/(FoodPercentBefore−FoodPercentAfter))

Now that we know the total volume before and after feeding, and the foodpercentage before and after feeding, we can also calculate the foodvolume before and after feeding:

FoodVolBefore=VolBefore*FoodPercentBefore

FoodVolAfter=VolAfter*FoodPercentAfter

In an exemplary embodiment, the measurement technique of usingconductivity, as well as conductivity combined with pH, can be combinedwith embodiments measuring the impedance of local tissue and fluids. Inthis exemplary embodiment, GRV is calculated using the impedanceapproach. GRV is also calculated using the conductivity approach,described and illustrated in FIG. 53-61 . The resulting calculationsfrom the impedance approach and the conductivity approach are thencompared to each other via an algorithm. An exemplary algorithm willcalculate the differences in the point calculations as well as thedifferences in calculations over time to determine an output signifyingif the calculations are within a determined tolerance of being inagreement or an indication they are not in agreement or not enoughinformation to determine if they are in agreement. The calculations mayalso be combined and/or smoothed by an algorithm using exemplarytechniques that can be utilized in this embodiment, including but notlimited to moving average, least squares, exponential smoothing, andLOESS/LOWESS regression. If the calculations are in agreement, this maybe indicated in the controller, potentially signifying a higherconfidence in the GRV and/or gastric emptying calculation.

In an exemplary apparatus, a common set of electrodes may be used tomeasure both impedance and conductivity. FIG. 22E shows an embodiment ofa GRV sensor composed of four electrodes in a tetrapolar impedancemeasurement configuration. For measuring GRV, the source electrodes are2205 and 2202 and the sense electrodes are 2206 and 2201. Theconductivity sensor in this embodiment can be composed of just twoelectrodes, 2201 and 2202, to simultaneously inject, or introduce,current and sense voltage forming a bipolar conductivity measurementconfiguration. In an exemplary embodiment, the conductivity sensor canbe composed of four electrodes. Electrodes 2201 and 2202 measureconductivity at the distal tip while electrodes 2205 and 2206 measureconductivity at the more proximal location on the tube. Thisconfiguration is similar to FIG. 53 , where electrodes 5304 areequivalent to electrodes 2201 and 2202, and electrodes 5312 areequivalent to electrodes 2205 and 2206. Each electrode combination maysimultaneously inject current and sense voltage forming a bipolarconductivity measurement configuration.

In an exemplary embodiment, the electrodes in FIG. 22 e and FIG. 53 canbe applied to a tube via conductive ink. Many different types ofconductive ink can enable effectively collecting this data. In anexemplary embodiment, the conductive ink used is AGCL-675 Silver/SilverChloride Ink provided by a company called Conductive Compounds. In theseembodiments, the conductive ink is printed or otherwise applied directlyto the surface of the feeding tube.

In an exemplary embodiment, pH is also calculated and used by anexemplary algorithm along with the impedance based calculation andconductivity based calculation of GRV. The algorithm would combine thepH measurement with the impedance and conductivity GRV measurements todetermine a combined measurement or indication of GRV.

Some embodiments of the GRV measuring device may include feeding tubekink detection mechanisms, to detect if/when the feeding tube kinks, ordoubles back on itself during placement, and also to detect if/when thetube become kinked after placement.

Some embodiments of the GRV measuring device may include a retentionmechanism, such as a retention balloon to keep the feeding tube in placeafter it is placed. The retention mechanism may be moveable with respectto the feeding openings of the feeding tube e to adjust to differentsize stomachs etc. The retention mechanism, such as a balloon, may belong, and/or only on one side of feeding tube so that some segment ofthe balloon is in the esophagus. In cases where the sealing mechanism isa balloon, the balloon may be compliant or non-compliant. The balloonmay be a low pressure balloon. FIG. 62 shows an embodiment of the GRVmeasuring device with retention balloon 6202.

Some embodiments of the GRV measuring device may include the ability totest whether the feeding tube is bent or kinked. In one embodiment, thecontroller may introduce pressurized fluid (gas or liquid) into a lumenof the feeding tube and measure the pressure required for the fluid toflow through the lumen. A baseline pressure may be detected on anon-bent feeding tube to determine the unkinked pressure range. If/whenthe tube is bent or kinked, the pressure required will increase. Thecontroller can measure and track this pressure over time and candetermine the status of the feeding tube based on the absolute pressure,the relative pressure, the change of pressure or the slope of change ofpressure over time.

Bending or kinking of the feeding tube may also be measuredelectronically, for example by measuring the proximity of the electrodesto each other. If the electrodes are closer to each other than theirspacing along the feeding tube, then a kink or tight bend is likelypresent in the tube. This can be done by measuring impedance and/orconductance between electrodes. The pairing of electrodes can be changedby the controller to determine GRV vs electrode proximity.Alternatively, the same electrode pairing may be used.

For example, see FIGS. 63 and 64 . FIG. 63 shows a GRV measuring devicewith pH sensor 6302, openings (for feed) 6304, electrodes 6306 whichinclude electrodes 1, 2, 3, 4, 5, 6, 7, and 8. Electrode pairs 1 and 2,3 and 4, 5 and 6, and 7 and 8 are used as pairs during feeding andplacement of the feeding tube to determine conductance/impedance at theelectrode pair. However, different electrode pairs may also be used. Forexample, electrodes 1 and 6 may be used as a pair. The distance betweenelectrode 1 and 6 can be determined via conductance/impedance. When thedevice is relatively straight, the distance between electrodes 1 and 6is Z. If the distance becomes shorter, as in Z′ shown in FIG. 64 , thecontroller can either sound an alarm/alert, or automatically attempt anunkinking procedure to attempt to unkink the tube. Note that thedetection of a kink may involve any electrode pair and the pair'srelative distances from each other. For example, theconductance/impedance between original electrode pairs may not change inthe presence of a kink, but the conductance/impedance between electrodepairs which are further apart may change. The combination may indicate abend/kink situation.

ECG signal may also be detected by the electrodes on the GRV measuringdevice to determine the location of the tip, or other area, of thefeeding tube relative to the heart—this may be used to help withplacement of the feeding tube and also to detect kinks.

The electrodes may also be used to detect the electrical state ofstomach muscle. A myoelectric signal, for example, may be detected todetermine tube placement and tube kinks.

Anatomical pressure may also be measured using the GRV measuring device.Anatomical pressure may be measured through a feeding tube lumen, and/orvia balloons or pressure sensors on or in the feeding tube to determineplacement within the anatomy.

The GRV measuring device may be straightened, or stiffened, during orafter placement, by blocking the feeding hole(s) with a balloon,balloons, valve(s) or other mechanism. The inner lumen of the feedingtube may then be pressurized to make it more rigid. Alternatively, aballoon may run inside the feeding lumen, or within another lumen, or onthe outside of the feeding tube to stiffen/straighten the tube.

A variable durometer feeding tube may also be used to prevent kinks andhelp with placement. For example, the feeding tube of the GRV measuringdevice may be softer toward the stomach end.

A guide sheath may be used over the feeding tube portion of the GRVmeasuring device to control the durometer of the feeding tube during andafter placement or to unkind the tube. The guide sheath may be slidableover the feeding tube to change the relative rigidity of differentportions along the tube's length.

A guide stylet may be used inside a lumen of the feeding tube portion ofthe GRV measuring device to control the durometer of the feeding tubeduring and after placement or to unkind the tube. The guide stylet maybe slidable within a feeding tube lumen to change the relative rigidityof different portions along the tube's length.

The GRV measuring device may include a sheath or lumen which houses acamera or an esophageal scope to view tube placement.

It is desirable also to prevent biofilm and/or bacteria buildup on andin at least the feeding tube portion of the GRV measuring device. Thiscan be achieved by using anti-bacterial coatings and/or impregnating thedevice materials with anti-bacterial materials. For example, the feedingtube portion may be made from a material impregnated with Silver, or maybe coated with Silver or any other antibacterial material. Thecoating/material may be only present on the inside of the feeding lumen.

In an exemplary embodiment, the electrodes and wires in FIG. 13 , FIG.22 e and FIG. 53 can be applied to a tube via conductive ink containingsilver, such as AGCL-675 Silver/Silver Chloride Ink provided by acompany called Conductive Compounds. In this embodiment, the conductiveink impregnated with Silver may sufficiently provide an anti-bacterialeffect.

UV, or other wavelength, light may be used inside the lumen of thefeeding tube to disinfect the lumen. For example, a light fiber may beinserted within the feeding tube lumen and UV light shined inside thelumen between feedings. This may be done manually, or automatically. Thelight fiber may be inserted and removed between feedings or remain inplace during feedings.

The feeding tube lumen may be flushed between feedings with saline, anantibacterial flush or other suitable flush. The flushing fluid mayenter the stomach or may be circulated (introduced into the lumen andremoved from the lumen) so that none, or very little, enters thestomach. The introduction and removal of the flushing fluid may both bedone through a single lumen or through more than one lumen. For example,the flushing fluid may be introduced and then sectioned out, or forcedout with another fluid (liquid or gas). Alternatively the flushing fluidmay be introduced through one lumen, and retrieved through anotherlumen. For example, the feed openings may be sealed or blocked from theflushing fluid with a balloon, sealing mechanism, valve etc. FIG. 65shows a cross section of a feeding tube of the GRV measuring device withflush introduction lumen 6502 and flush retrieval lumen 6504. Duringfeeding both lumens may be used to supply feed. Between feedings, thefeed openings may be blocked and flushing fluid may be introducedthrough lumen 6502. Lumen 6502 is in fluid communication with lumen 6504above the blocking of the feed openings so that the flushing fluid canthen be retrieved via lumen 6504. This flushing process may be donemanually or automatically by the controller between feedings.

Simple manufacturing and cost reduction of the GRV measurement device isalso desirable. The electrical connections for the electrodes may be viawires, or electronically conductive ink which is printed onto the tubeshaft. The connections may be on the outside of the shaft, embedded inthe wall of the shaft, or in a lumen of the shaft. In one embodiment,electrical wires are between concentric tubes of the feeding tube shaft.In this configuration, they may be fixed in place, or allowed to floatfreely in the space between the tubes.

FIG. 66 shows an embodiment of the GRV measurement device with outertube 6602, inner tube 6604 and electrical wires 6606. The electricalwires are between the inner and outer tube, and connect to thecontroller on one end, and electrodes and/or pH sensors on the otherend.

FIG. 67 shows an embodiment of the GRV measurement device with wire (orwires) 6702 within the feeding lumen 6704. In this embodiment the wiresor other electrical connection is inside the feeding lumen and may alsobe used for sterilization of the feeding lumen.

FIG. 68 shows an embodiment of the GRV measurement device withtelescoping tubing, each with one or more electrodes/sensors. In thisembodiment, the electrical connection, i.e. wire, may pass betweentubings similar to the embodiment shown in FIG. 66 . Electrodes 6802 maybe placed at or near the distal tip of each tube making them easier tomanufacture.

Electrical connections may also be made with wires, or braids embeddedor coextruded in the feeding tube tubing. Conductive polymer may be usedfor electrodes for easier, less costly manufacturing.

The pH measuring device may be a separate device, such as a guide wireor stylus with a pH sensor at the tip, which is used only tube placementand then optionally removed for feeding so that wiring for the pH sensordoes not need to be incorporated into the feeding tube.

PH measurements may be obtained by using 2 electrode rings of dissimilarmetals by measuring electron flow between the 2 electrodes.

Balloons or other spacers may be incorporated into the GRV measurementdevice at, or near, the electrodes to prevent the electrodes fromcontacting the stomach wall.

Neuromodulation may be used to induce contractions where the mobility ofthe stomach is slow (gastroparesis). The electrodes, or other electrodesmay be used for this, by energizing them in sequence to stimulate thestomach/intestine/esophagus wall. The optimal frequency, or nearfrequency, would be that of natural peristaltic waves.

All embodiments disclosed herein may incorporate features from otherembodiments disclosed herein. An automatic feedback loop may be used toautomatically provide the right amount of feed to a patient, based onGRV measurements. The GRV measurement system may include an audible, orother type of, alarm when the volume of food within the stomach isunacceptable. The feeding tube may incorporate a pump, flow system,pressure system or other system to help clear the feeding tube of clogsif they occur. A clog detector may be incorporated into the system.

What is claimed is:
 1. A tubing assembly comprising: a catheter having aproximal end and a distal end and extending in a longitudinal direction,wherein the proximal end and the distal end define a lumen therebetween,and wherein the catheter is configured for placement within a digestivetract of a patient; and an acoustic sensor.
 2. The tubing assembly ofclaim 1, further comprising a multi-port connector comprising a nutrientbranch and a branch for introduction of a second fluid.
 3. The tubingassembly of claim 1, wherein the acoustic sensor is located within thelumen of the catheter.
 4. The tubing assembly of claim 1, wherein theacoustic sensor is configured to acquire sound data from sound wavestraveling through the lumen from an opening in the distal end of thecatheter and communicate the sound data to a processor in real-time. 5.The tubing assembly of claim 1, wherein the acoustic sensor isconfigured for a wired connection or a wireless connection to theprocessor.
 6. The tubing assembly of claim 1, wherein the acousticsensor is one of an electret, condenser, piezoelectric crystal,piezoelectric ceramic, piezoelectric film, fiber optic microphone, orcontact accelerometers.
 7. A catheter guidance system, comprising: (a) aprocessor; (b) a power source; (c) a display device; and (d) a tubingassembly, comprising: a catheter having a proximal end and a distal endand extending in a longitudinal direction, wherein the proximal end andthe distal end define a lumen therebetween; and an acoustic sensor;wherein the acoustic sensor communicates sound data acquired by theacoustic sensor from sound waves traveling through the lumen from anopening in the distal end of the catheter to the processor in real-timevia an electrical connection; wherein the display device is coupled tothe processor and displays a graph of the sound data communicated by theacoustic sensor; wherein the catheter guidance system alerts a user asto correct placement of the catheter in a digestive tract of a patientor alerts the user as to incorrect placement of the catheter in arespiratory tract of the patient.
 8. The catheter guidance system ofclaim 7, further comprising a memory device storing instructions which,when executed by the processor, cause the processor to (i) interpret thesound data communicated by the acoustic sensor and (ii) cause thecatheter guidance system to alert the user as to correct placement ofthe catheter in the digestive tract of the patient or alert the user asto incorrect placement of the catheter in the respiratory tract of thepatient based on the interpretation of the sound data.
 9. The catheterguidance system of claim 7, wherein the acoustic sensor is locatedwithin the lumen of the catheter.
 10. The catheter guidance system ofclaim 7, wherein the acoustic sensor is one of an electret, condenser,piezoelectric crystal, piezoelectric ceramic, piezoelectric film, fiberoptic microphone, or contact accelerometers.
 11. A method fordetermining if a catheter is placed within a digestive tract of a bodyof a patient, the method comprising: (a) inserting a distal end of atubing assembly into an orifice of the body, wherein the tubing assemblycomprises: the catheter, wherein the catheter has a proximal end and adistal end and extends in a longitudinal direction, wherein the proximalend and the distal end define a lumen therebetween; and an acousticsensor; (b) electrically connecting the acoustic sensor to a processorvia a wired connection or a wireless connection; (c) activating theacoustic sensor, wherein the acoustic sensor acquires sound data fromsound waves traveling through the lumen from an opening in the distalend of the catheter and communicates the sound data to the processor inreal-time via the wired connection or the wireless connection; (d)advancing the distal end of the catheter inside the body in a directionaway from the orifice while the acoustic sensor is activated; and (e)observing a graph of the sound data on a display device coupled to theprocessor, wherein the display device alerts a user as to correctplacement of the catheter in the digestive tract of the patient oralerts the user as to incorrect placement of the catheter in arespiratory tract of the patient.
 12. The method of claim 11, wherein amemory device stores instructions which, when executed by the processor,cause the processor to (i) interpret the sound data communicated by theacoustic sensor and (ii) cause the display device to communicate whetheror not the catheter is placed within the digestive tract of the patientbased on the interpretation of the sound data.
 13. The method of claim11, wherein the orifice is a nose or a mouth.
 14. The method of claim11, wherein the acoustic sensor is located within the lumen of thecatheter.
 15. The method of claim 11, wherein the acoustic sensor one ofan electret, condenser, piezoelectric crystal, piezoelectric ceramic,piezoelectric film, fiber optic microphone, or contact accelerometers.